Cyclone Yasa, a top category five storm, is expected to bring winds of up to 250km/h and torrential rain across the South Pacific archipelago when it makes landfall.

Still a few hours out from the worst weather, Fiji's Meteorological Service said storm force winds and heavy rains have been recorded in some parts of the country already.

Images shared on social media showed roads blocked by landslides, floodwaters and fallen trees.

Yasa's centre is forecast to be 100km east of the village of Yasawa-i-Rara and potentially over Fiji's fifth-most populous province of Bua, home to 15,000 people, Fiji's National Disaster Management Office said.

Reinforcing the threat, Fiji Prime Minister Frank Bainimarama told the country's near one million population to find safe shelter ahead of a 14-hour nationwide curfew.

"The impact for this super storm is more or less the entire country," Bainimarama said in a video posted to Facebook.

Yasa would "easily surpass" the strength of 2016's Cyclone Winston, he added, referring to the southern hemisphere's most intense tropical storm on record, which killed more than 40 Fijians and left tens of thousands of people homeless.

The curfew order was given as part of the state of natural disaster order, which will run for 30 days.

More than 95 per cent of the population live in the direct path of Yasa, Bainimarama said, adding weather forecasts anticipated flash flooding and "severe coastal inundation" that included waves up to 10 metres high.

Fiji banned the running of public transport, and was taking precautions with some 50 foreign yachts moored in the southern part of the island chain.

Australian Associated Press