A powerful cyclone has hit Fiji, damaging homes and crops and forcing at least 5,000 people to flee to evacuation centres.

Cyclone Tomas is a category four cyclone, the second-most destructive on a five-point scale, with winds of up to 170 kilometres per hour.

It is reported to have generated waves up to seven metres high.

One death has been reported after a woman drowned in high seas at the weekend.

The director of Fiji's Disaster Management Authority, Pajiliai Dobui, says many who lived in the storm's path have been evacuated.

"About 5,000 are already taking shelter in most of the shelters of the northern division," he said.

The storm is moving slowly and is forecast to intensify and shipping has been warned to stay away from the islands.

Average wind speeds are expected to rise overnight to 200kph with gusts of up to 270kph.

Fiji's director of meteorology Rajendra Prasad says the cyclone is likely to only sideswipe the main islands, which are home to most of the population.

"Initially it looked as though it may be moving more south west for a while and that is why we actually had the whole of the country under warning," he said.

"Right now it is the same situation, but the category of the warning has been toned down, say for the western division."

A night-time curfew is in operation in northern and other parts of Fiji.

Inia Seruiratu, the head official in the northern region, says weather conditions worsened dramatically during Monday.

"You can see trees swaying and likewise the electrical wires and cables that are running between the poles," he told state radio, adding that conditions would be worse in other areas.

Officials say communications have been lost with smaller islands closer to the eye of the cyclone.

One resident, Alifereti Fisaitu, says his town has escaped damage but others were not so lucky.

"We have got news from some of our relatives that entire villages, called Wainiika, Nuku and Vatu, are all under seawater and the villagers have fled to an evacuation centre," he said.

The eye of Cyclone Tomas was expected to pass to the east of Vanua Levu and the largest island Viti Levu, although many smaller islands will be close to its path.

Schools have been closed and most public services suspended throughout the country.

Cyclone hits Solomon Islands

Meanwhile, emergency officials in Solomon Islands were keeping watch on Tropical Cyclone Ului, which hit its southern provinces Sunday night.

There have been few reports of major damage and no reports of any lives lost.

The cyclone is in the Coral Sea, more than 1,400 kilometres north-east of Mackay in north Queensland, and is moving slowly west-south-west.

The weather bureau says it is unlikely to pose a threat to the Queensland coast.