Fiji declared a nationwide curfew today, as airlines suspended flights and the prime minister warned people to seek refuge from a cyclone that could prove to be the Pacific island nation's most powerful on record.

After twice hammering outlying islands in nearby Tonga last week, Cyclone Winston re-intensified and began to track west towards Suva, the capital of Fiji, packing winds of 230 km/h, with gusts of up to 325 km/h.

Prime Minister Frank Bainimarama urged Fijians to prepare themselves for a "terrible event", Australian broadcaster ABC reported.

"We cannot afford to be complacent," it quoted the prime minister as saying.

"And I am especially concerned that some people in urban areas do not appear to have heeded the warnings about the seriousness of the threat."

"A total public curfew will take effect across the country today from 6pm," a statement on Facebook said.

As Fiji's weather service warned people in the east to "expect very destructive, hurricane-force winds," Suva resident Alice Clements said the power had failed and she expected water supplies to be hit next.

"I have palm trees flying all around me at the moment," Ms Clements, an official with a UN agency, said.

The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said Winston was following a path that might spare Suva the full force of its winds, rated as category 5, the highest ranking on the hurricane wind scale.

"The cyclone has tracked further north than expected over the past 24 hours," the UN agency said.

Airlines Virgin and Jetstar suspended flights into and out of Fiji's international airport at Nadi, while the national carrier suspended all flights.