UPDATED 8.34PM The Fijian Government has confirmed Cyclone Zena, due to hit Fiji tonight, has been upgraded to a category three.

Flooding has already taken one person's life -- a 70-year-old man -- and a 19-year-old girl is still missing on the Sabeto River near Nadi.

The towns of Nadi, Lautoka and Ba are closed.

Habitat for Humanity said it's already evident a clean up will be needed, just how big-a-clean-up is unknown.

CEO Claire Szabo said Zena has gained momentum quickly, threatening the temporary housing in place.

"It just reminds New Zealanders again that the support is really needed in Fiji. Any help that people can give that would be incredibly appreciated".

Cyclone Zena comes just six weeks after cyclone Winston killed 36 and displaced tens of thousands of others.

Greenpeace Pacific's Matisse Walkden-Brown told Larry Williams cell phone coverage and power is intermittent.

"The winds have definitely picked up and it feels like a cyclone is on its way. Here in Nadi we definitely haven't seen the peak yet but the worst is still yet to come".

LISTEN ABOVE: Greenpeace's Matisse Walkden-Brown talks to Larry Williams 

Walkden-Brown said heavy rains and winds of more than 200 kilometres an hour are expected.

"It's just stopped raining now after drizzling all day and we're being told to brace ourselves for heavy rainfall in the next few hours".

Lieutenant Colonel Mike Van Welie said at the moment their three helicopters can still get supplies to where they're most needed.

"The next 24 hours we will continue some of those tasks but at the moment there's not much we can do apart from wait for the storm to pass".

Flights, departing and arriving have been cancelled and the Government's imposed a 6pm curfew.

Air New Zealand cancelled today’s return service to Fiji as Cyclone Zena draws closer.

An airline spokeswoman has confirmed flights NZ752 and NZ753 have been cancelled. 

The Fijian government's told it's more than 800 schools to close tomorrow because of Cyclone Zena.

Two severe depressions have caused flooding over the past week mainly in the western part of the main island Viti Levu.

SEE ALSO: Two tropical depressions expected to hit Fiji

Radio Fiji's Indra Singh said most of the places devastated by Cyclone Winston a little more than a month ago, are going to be hammered again.

"Ba, Nadi, Lautoka, Sigatoka, most of the place in these areas are all under water now and closed off to the public. It's not ready for another natural disaster so soon after Cyclone Winston"

Singh said everybody's worried about what's going to happen, but they've "been warned by authorities to take precautionary measures".

"Most of them moved up to the evacuation centres on Monday when when the flood water started to rise, so they are still there.

"They expect a lot more to move in, and mind you some people are still in evacuation centres from tropical cyclone Winston because they had everything destroyed."

Red Cross spokeswoman Corrine Ambler said the problem is, the country is still picking up the pieces from category five Cyclone Winston. 

"I was out in the field myself last week when I saw some of the structures they are living in and sheltering under and I can tell you they are not going to withstand the rain that we've had in the 3 days, let alone the cyclone that is coming."

Unicef's Alice Clements is in Suva and said the rain and the wind have picked up, but the rain is the biggest concern.

She said after Cyclone Winston, people returned to corrugated iron and tarpaulin shacks that are already falling apart.

"We're seeing rivers break their banks and entire communities standing in waist high or even deeper water. So if they're in temporary shelter that's not going to stand up to this onslaugther".

Habitat for Humanity CEO Claire Szabo said over 3500 people have been evacuated.

"People have already been displaced from their homes perhaps they're in temporary shelters that we might have been able to patch up and now it's looking like those are going to be under threat again".

Ambler said the floodwater could be very dangerous even if it looks safe.

She said people are being urged not to swim or cross waters which could be contaminated or flowing faster than they think.

Clements said in addition to the immediate risk of people being swept away by flood waters, a wave of infectious diseases could also take hold given the country is still recovering from Cyclone Winston.

"In times of extensive flooding and prolonged rain we see quite a sharp increase in respiratory infections, skin infections, eye infections, like conjunctivitis, the spread of diarrhoea and also the spread of mosquito borne diseases".

Ambler said the Red Cross won't reach some areas until Friday or Saturday.

High tide is expected just after five o'clock tonight.