Stunned mums and their tots at a riverside playground cowered as a car sailed over their heads during a spectacular deadly crash in Warkworth yesterday.

Locals are marvelling no one else was accidentally killed or injured as the out-of-control vehicle launched through an area that was only a few minutes earlier packed with people.

At least two families were forced to take evasive action as the speeding car became airborne, flying over a public playground before crashing down into a bench seat and fence, and sinking into the Mahurangi River.

Despite heroic efforts bystanders who plunged into the water could not save the driver.

A Warkworth local, who the Herald agreed not to name, said those in the playground directly underneath the path of the car were left shaken, and described it as a surreal experience.

"It was like a movie set," said the man.

"Seeing a car come mid-air over a playground was just something you see in a stunt scene.

"They couldn't believe it."

He said before the car launched over the play area, it had been picking up speed as it headed towards the river in a line of devastation.

"The car came straight down the hill at high speed over the roundabout mid-air, bounced down, past the public toilets in a straight line, straight through the car park, missed a tree by 50cm, over the top of the playground and two families, down onto a chair at the bottom and through the fence and into the river.

"The girl I know who was sitting in the playground, she was shocked and freaked out with her daughter. They pretty much dropped to the ground. Her mother ran and jumped in the water. She was the first one on the scene, but no matter how hard she tried she couldn't get the door open."

The car launched over the playground before plunging into the Mahurangi river. Photo /Supplied

Hawkings said the spot was very popular with walkers and parents alike.

"It's just amazing no one else was hurt. It was sheer luck no one else was walking. Normally that place is full of people - and it was - but they were just all out of the way just at the right time."

A woman who was with her young family preparing to have a meal on the riverbank said it is nothing short of a miracle carnage on a far larger scale didn't unfold yesterday evening.

"We were literally seconds away from a more expansive tragedy. With the amount of people that were in the car's route and to all miraculously move to the side within seconds of the car coming through was truly a miracle," she said.

"The boys and I had just turned the top right corner of the park when I heard what sounded like a car crash and a thought flashed to my mind, 'Oh no, someone's crashed into our parked car' and turned around to see a car hurtling down the small car park area. Then we all saw it fly over the playground and turning on its side while it was airborne and hit the water. It sunk very fast."

The woman, who did not want to be named, said she went to check on her partner, hoping she wouldn't find him injured in the parking lot.

"He told me he saw the car coming like a bat out of hell flying over the small roundabout but he thought the driver would slam on the brakes or hit some of the parked cars in the parking lot. But he quickly realised that the car wasn't stopping and was making a beeline for the playground. He was about two metres away from the car when it passed him at full speed."

She said only moments earlier she had called back her youngest who wanted to go play in the playground, running towards an open gate as others were coming out.

"It was very frightening for us especially, because we keep thinking if we were half a minute behind time, the outcome for us would've been catastrophic. It was under a minute that we were all lucky to be in safe positions during the car passing."

The woman praised the three bystanders who risked their own lives by jumping into the river to try save the driver's life.

The driver of the car, it's sole occupant, was understood to be a local resident.

Police have not yet released the driver's name.

Hawkings said the playground and stretch of riverside walkway remained cordoned off today.

Crash debris still littered the playground, including parts of the crashed car.

Police have not yet released the name of the man involved in the crash, confirming yesterday one person had died.

The Serious Crash Unit was investigating the cause of the accident.