Flood-ravaged Fiji declared a state of emergency Sunday and warned tourists to stay away for the time being, as heavy rain and high winds continued to pound the South Pacific nation.

Officials said they could not guarantee visitors' safety in the wake of flash floods that have killed at least two people and forced more than 5,000 to take shelter in evacuation centres.

With roads to the international airport in Nadi cut off and extreme weather expected to continue until Tuesday, officials asked airlines not to bring in any more tourists until Monday at the earliest.

"This action is being reluctantly taken by the Fijian government to ensure the safety and convenience of international visitors and Fijian citizens seeking to return to Fiji," Tourism Minister Aiyaz Sayed-Khaiyum said.

The request is believed to be unprecedented for tourist-dependent Fiji.

National carrier Air Pacific said it had cancelled all inbound flights scheduled for Sunday and was operating only limited outbound flights for passengers who had already checked in at Nadi airport.

Airports Fiji Limited chief executive Tony Gollin said hundreds of international passengers were at the airport awaiting departure.

Many more have been unable to reach the airport, in the west of the main island Vita Levu, after fallen trees, landslides and swollen rivers cut road access.

The government declared a state of emergency in flood-affected areas, saying the move would make coordinating flood relief more effective.

"It's all about efficiency, allowing all parties to just go in there and get going," a government spokeswoman said.

Police and the military were helping coordinate clean-up efforts but the ferocious weather meant that in some areas makeshift repairs to damaged homes were torn apart almost as soon as they were completed.

The entire centre of Nadi was declared off limits to the public because police said the force of water running through the streets after the town's river burst its banks threatened to sweep people away.

The latest flood disaster comes after a six-day deluge in January claimed 11 lives.