UPDATED 7.25pm French interior minister Bernard Cazeneuve told media 84 are people dead, including children, and 18 are in intensive care, after a truck ploughed into crowds of 40,000 in Nice.
LISTEN: Our French correspondent Robert Harneis talks to Larry Williams
Reports from Nice say a 31-year-old French-Tunisian man was driving the truck, after identity papers were found in the vehicle.
According to The Guardian, reports said the driver was known to police, but not for terrorist-related activity.
The French Interior Minister has confirmed the truck driver is dead.
The driver is reported to have picked up speed to slam the lorry into revellers.
French president Francois Hollande said it was an act of terror that “cannot be ignored” and this is “of absolute horror and it is clear that we have to do everything to ensure that we can fight against the scourge of terrorism”.
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He said: “France has been struck on the day of her national holiday, the symbol of liberty. We show our solidarity towards the victims and their families. All means are being deployed to help the wounded.
“France as a whole is under the threat of Islamic terrorism. We have to demonstrate absolute vigilance and show determination that is unfailing.
“France is afflicted but I assure you she is strong and she will always be stronger than the fanatics that want to strike her today.”
Cazeneuve said the police were being mobilised to identify the man behind the attacks and establish if he had any accomplices.
The national state of emergency, which was supposed to end on July 26, has been extended by three months.
Hollande said he would go to Nice on Friday [French time] to support the city.
“France is horrified by what has taken place, this monstrosity of using a truck to deliberately kill dozens of people who had come to celebrate 14 July,” Hollande said.
The French government has called for the cancellation of all events scheduled in Nice in the coming days.
Le Figaro reported 100 people who fled to the sea during the attack have been recovered.
Dawn revealed pools of dried blood, smashed children’s strollers, an uneaten baguette and other debris strewn about the promenade, according to Reuters.
What appeared to be bodies covered in blankets were visible between the gaps in security screens.
Pictures from the scene show people screaming, running and others lying on the ground.
Luxury hotel Negresco has been turned into a field hospital, with people crowding the lobby, some receiving treatment to injuries.
Laurence Marie from the Lenval paediatric hospital has told Reuters news agency that "many" children were undergoing serious operations there.
CNN's Becky Anderson said this would be the busiest spot in Nice on Bastille Day.
"This is the height of the summer period - the promenade is an area that will be packed on the 14th of July."
France correspondent Catherine Field told Larry Williams a former mayor of Nice is raising questions about why the truck could even get to the promenade.
"After all, this is the main beach front road that's supposed to have been closed off, particularly on Bastille night. Thousands of people go down there to watch the fireworks."
CNN's Jim Sciutto said the truck was able to drive through people for nearly two kilometres, travelling at about 40 kilometres an hour, running people down.
"Ambulances are now spread throughout that waterfront there, taking care of the injured, sadly taking care of the dead as well."
Eye witnesses say some people were hanging onto the door of the truck trying to stop it, and terrified people ran screaming as bodies flew everywhere.
One man says the truck was zigzagging everywhere so people didn't know where it was going next. He said his wife was killed just metres from him.
Iranian journalist Maryam Violet told the Guardian: “Everyone was completely shocked, I saw that suddenly people were fleeing and shouting.
“People were shouting, ‘It’s a terrorist attack, it’s a terrorist attack’, it was clear that the driver was doing it deliberately.
“I was walking for nearly a mile and that there were dead bodies over the place. I think over 30 dead bodies are on the ground and lots of people are injured.”
Tony Molina was watching the fireworks from the balcony of a hotel about 40 metres away from where the truck ploughed through people on the boardwalk.
He told CNN it looked like the truck deliberately drove into people at about 40 to 50 kilometres an hour.
"They were screaming and running everywhere and the very sad part is that there's still people, I'm looking at them right now and I believe they're near their deceased family members, just some people ran back basically screaming."
"Dear Nicois," local government leader Christian Estrosi wrote in a tweet. "The driver of a truck appears to have killed dozens of people. Stay at home for the time being. More news to follow."
Regional newspaper Nice Matin quoted its reporter at the scene saying there were many injured people and blood on the street.
It published a photograph of a damaged, long-distance delivery truck, which it said was "riddled with bullets" and images of emergency services treating the injured.
Damien Allemand, the paper's correspondent, was quoted as saying: "People are running. It's panic. He rode up on to the Prom and piled into the crowd... There are people covered in blood. There must be many injured."
Hali Rose McField is near the scene and said: "A couple of people first started running and initially I didn't think it was that big a deal, and then there was a whole crowd of people filling up the street, just running. They were yelling stuff and I got really scared."
Facebook has enabled safety check to allow people in the area notify friends they are OK.
Is it terrorism?
Field said police are being very cautious, using the word attack but not terrorist.
However she said it's important to remember an eerie prediction made just over a week ago from a senior member of the French internal intelligence agency.
"He feared young people inspired by the so-called Islamic State would be changing their tactics. They would be moving away from the thought of open shooting of people as we saw on the streets of Paris last November, to more lone wolf type attacks."
The French public prosecutor has confirmed the investigation has been taken over by anti-terrorist investigators.
CNN terrorism analyst Paul Cruickshank said the fact weapons and explosives have been found in the truck, makes it sound as though it was planned.
"The goal in these attacks is to kill as many people as possible, to injure as many people as possible. They want all of this to be in the global headlines for as long as possible."
He said if the attack was carried out by ISIS, "we can expect some claim of responsibility fairly soon." He stressed however that the culprits were not yet known.
CNN's Anderson Cooper said anti-terrorist investigators will now be looking into whether the man acted alone - and if he did, why he was carrying so much extra artillery.
"If there were explosive, weapons, grenades in the truck, why wouldn't those have been used by others - if there were other co-conspirators."
LISTEN: "Intelligence authorities knew this was coming" Catherine Field on the latest attack in France
Local authorities were treating the incident as an attack, almost exactly eight months ago Islamic State militants killed 130 people on a Friday night in Paris in November.
New Zealanders in France
New Zealanders in Nice are being advised to stay away from the area and follow the instructions of authorities.
SEE ALSO: Christchurch high school students confirmed safe in Nice
The Ministry of Foreign Affairs and Trade says people should contact their family in New Zealand to advise that they're safe.
People with concerns about a New Zealand citizen family member in France are asked to try to make direct contact with them in the first instance.
Anyone with ongoing concerns is asked to contact MFAT on 04 439 8000.
Meanwhile, the New Zealand Embassy in Paris has sent out an alert for the 882 New Zealanders registered as being in France.
They're being invited to call the embassy on 01 45 01 43 43 if they require consular assistance.
Any people in France who aren't registered on SafeTravel.govt.nz are being strongly urged to do so by the ministry.
New Zealand's Embassy in Paris is working with local authorities to find out if any New Zealanders have been harmed.
Prime Minister John Key issued the following in a statement on Twitter:
“Our thoughts are with the victims of the tragic events in Nice, their families, and the people of France."
Key then passed on his condolences to the President and Prime Minister of France following today's terror attack in Nice.
Attacking innocent people celebrating their national day made it "particularly horrific", Key said.
“No one should have to worry about such violence when going about their daily lives. I know the thoughts of all New Zealanders will be with the victims and their families at this sad time."
In earlier discussions with the President and Prime Minister they affirmed the joint commitment of New Zealand and France to the international campaign against terrorism.
“Today I reiterated New Zealand stands shoulder to shoulder with France in combating violent extremism."
Officials from the Ministry of Foreign Affairs and Trade were working to determine if any New Zealanders had been caught up in the attack, Key said.
"We encourage New Zealanders in France to make contact with loved ones directly to confirm their well-being."
Key was with Australian prime minister Malcolm Turnbull at the Australian Embassy in Paris watching the fireworks when the attack took place.
He told Larry Williams an ambassador informed them about the attack and a short time later the embassy was put into lockdown.
"There was sort of controlled explosions of cars about 30 minutes later, initially they sounded like fireworks, but they were cars they were obviously concerned about."
United Nations development programme head Helen Clark described today’s attack in Nice as shocking and distressing.
“Shocking news fm Nice #France where lorry ploughs in2 #BastilleDay crowd causing death & injury. Sincere condolences,” she posted.
Initial reports were distressing and it was a shocking attack on a crowd gathered to celebrate their national day, she said.
A Kiwi woman whose twin is believed to be in Nice says she won’t relax until she hears her sister is ok.
Val Feisst, of Cambridge, has been waiting anxiously all morning for a Whatsapp message from her twin sister Enid Limmer.
Enid left Hamilton for France to see the Tour de France with her husband a couple of days ago.
Ms Feisst was feeling “a bit apprehensive,” saying she hadn't heard anything in the last few hours.
She said her sister has a daughter and a son over here and they all want to know she's okay.
Heather from Upper Hutt is in shock, with her daughter and son-in-law currently in Nice on an overseas holiday.
She says the pair were 800 meters away when the attack happened.
"They had just been to the beach, and next thing there were sirens. They were in such shock they just ran, and they've never run so fast in their life and they just crouched down behind a building."
"We just want them back home."
St Helier's man David Boyd arrived at his hotel at the Promenade des Anglais two hours before the attack.
In a potentially life-saving decision, he watched the fireworks display from his hotel rather than on the heavily crowded promenade, he told the New Zealand Herald via email.
"The terrorist certainly knew when to make the maximum impression, just like a high speed truck would be into the start of Round the Bays.
"I did not expect Nice to be in a terrorist's sights, it shows nothing is safe. New Zealand is still a good place and I look forward to returning in three weeks."
House of Travel says those planning to travel to Nice in the next few days will be advised on a case-by-case basis.
Commercial director Brent Thomas said they'll work with customers to alter their travel plans if need be.
"We'll work with suppliers, if the customer wants to change their itinerary, to see if we can make that happen."
He said they're currently in the process of contacting those already in Nice and ensuring their safety.
New Zealand travel agent helloworld is also trying to ascertain the safety and welfare of its clients that have been in Paris or Nice.
Marketing general manager David Libeau said they know of a few customers who may be in Paris or Nice and they're trying to contact them to ensure they are safe.
They're also offering those customers any assistance with altering their travel plans.
Contiki Tours said all its passengers are safe and accounted for in Nice.
Spokesman Gordon Gillan said they have four tour groups there but he can't say how many Kiwis are among them.
He said some New Zealanders may have booked tours from other parts of the world.
He also can't confirm the exact number of people they have on tour in Nice.
Australians in France
The Daily Telegraph is reporting that three Australians have been injured in the terrorist attacks in Nice. Foreign Minister Julie Bishop confirmed all three suffered minor injuries while fleeing the horror.
"We join with others around the world in hoping that this will be the end of this type of horrific incident, that is targeted at unarmed civilians," Ms Bishop said.
One of the injured Aussies was a woman on a Topdeck tour, the tour company confirmed.
An Australian tourist in Nice posted a series of photos taken along the promenade minutes before the attack.
The photos taken by Marcus Freeman showed packed crowds of people along the promenade and on the beach.
His first post to Facebook following the attack reflects his confusion.
"Just got back from the Bastille day celebrations in Nice and not sure what just happened?!!! Reports are that a truck crashed into the crowd, however we were 15m from our hotel when we heard what sounded like gunshots and people fleeing everywhere! We raced into our hotel...waited for lift (longest wait of my life)...then I steered around 10 people up with us. Scary times and will wait for further reports. I am hoping/praying it was all just panic and no-one was hurt."
Later he posted that he and others were in lockdown in their hotel.
"Words cannot describe the fear...we collected 10 x people from the street and brought them into our hotel. Very sad and cannot believe this has happened...I commented earlier in the night how everyone was so happy and well behaved...such a great feel to the place."
By the early hours of the morning Freeman's shock was still palpable.
"It is very surreal and we are so sad for those who lost their lives...many were beautiful little kids. The next few days will be tough and getting back to our daughter in Paris is priority 1. What is the world coming to?"
Australian Prime Minister Malcolm Turnbull has offered his condolences to the French people following the deadly Bastille Day attack.
He's currently in Paris with John Key where they have attended the Bastille Day Parade.
In a statement, Mr Turnbull said they're mourning for the victims of yet another murderous act of terror.
He said Australia, New Zealand and France are united in the cause of freedom as they were a hundred years ago this week.
Mr Turnbull said John Key has told him he was enormously proud to see the ANZACS lead the Bastille Day Parade overnight.
The French flag is flying above the Sydney Harbour Bridge in a show of solidarity.
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