Weather: Cyclone Yasa makes landfall on Vanua Levu, Fiji

Severe Cyclone Yasa has made landfall on Fiji, with wind gusts up to 345km/h threatening to decimate the island nation.

The category 5 storm was initially due to hit Vanua Levu - Fiji's major northern island - at about 9pm (NZ time), however, it struck about an hour earlier than expected.

MetService Fiji duty forecaster Amit Singh confirmed the cyclone's landfall to Newshub on Thursday evening.

"The cyclone has made landfall over Vanua Levu, and Vanua Levu is experiencing category 5 winds at the moment. But for the western division it's just gale force winds," he said.

Fiji's National Disaster Management Office (NDMO) earlier declared a state of natural disaster, which is in addition to a nationwide curfew that's set to last from Thursday 4pm to Friday 6am (local time).

NDMO director Vasiti Soko says the declaration allows the office to efficiently and effectively plan and coordinate the response for Cyclone Yasa.

"It will also assist NDMO and government ministries and departments to manage and control activities to ensure the safety and security of the public," she says.

The declaration means people can be evacuated, properties can be entered or searched, essential relief supplies, medical assistance, shelter, or other resources can be supplied, and land, sea, and air services can be maintained, among other regulations.

MetService Fiji says close to the centre of the cyclone is expected to have winds of up to 240km/h, with wind gusts to 345km/h. Waves up to 16 metres high are also expected as the cyclone makes its way through the country.

By 8am on Friday, the centre of Cyclone Yasa is expected to be 50km northeast of Moala Island or about 165km east of Suva, Fiji's capital.

MetService Fiji warns residents to expect periods of heavy rain and thunderstorms. There's also a risk of flash flooding in low-lying and flood-prone areas, and landslides "are likely" with continuous heavy rain.

This cyclone is the fourth most powerful tropical cyclone recorded in the South Pacific region, according to WeatherWatch.

Earlier on Thursday, the forecaster said this storm is so powerful that it "has the ability to swamp entire islands, inundate entire coastal communities, wipe some small islands off the map entirely, destroy buildings, bring down trees and cause slips and flooding".

"The most destructive part of this cyclone will be 150km either side of the centre. Heavy rain will affect the entire region - and has done so for the past day. 250-300mm of rain is possible over the next two days."

The rain radar from Fiji's MetService did show the cyclone moving in, but the signals have since gone down which WeatherWatch assumes is from power outages on Vanua Levu.