Cyclone Winston has hit landfall in northern Fiji and has reportedly claimed its first victim.
Fiji radio reported an elderly man died after a house collapsed on him.
WeatherWatch confirmed the development about 8pm, with the Category 5 cyclone lashing Viti Levu - Fiji's main island - with winds of 230kmh, gusting to 325kmh.
Waves around the eyewall of the storm are 12m high at sea and expected to grow. Flooding in coastal areas is predicted.
"The centre of the storm is now tracking directly towards Nadi - but the mountains of Fiji may help weaken the system now that the eye is no longer feeding off the warm sea," WeatherWatch head analyst Philip Duncan said.
"The centre of Cyclone Winston is likely to track very near, or possibly even over, Nadi around dawn, which is concerning to the many people there".
Cyclone Winston is Fiji's strongest storm in recorded history.
The storm also peaked in strength just as it approached Fiji from the east.
It is expected to gradually start to weaken to a Category 4 cyclone overnight and into Sunday, as it moves over Fiji.
"We believe it may weaken faster due to its last minute track further south over land, but flooding, slips, destructive winds and significant storm surges are all likely overnight tonight, especially in the northern half of Viti Levu" Mr Duncan said.
It is still too early to know how and if Winston will affect New Zealand.
Mr Duncan said more information on Cyclone Winston's future once it's left Fiji, either late Sunday or early Monday.
Meteorologists believe the tropical cyclone is "the biggest and fiercest storm in the world right now" and fear it could be a killer.
Some islands have been evacuated and flights and sailings cancelled.
The Fijian Government has declared a state of natural disaster.
"The Government machinery shall now roll into place to ensure the safety of members of the public, businesses, our economy and national assets," Meleti Bainimarama, Fiji's natural disaster secretary has announced.
Mr Bainimarama said the declaration will be in effect for the next 30 days.
The Government has also issued a total public curfew across the country from 6.00pm.
Fiji's National Disaster Management has advised that a total curfew will take place until further notice.
The latest measure is designed to restrict movement and ensure the safety of all Fijians. Only essential services will be permitted to travel.
Video footage emerged of the Spanish men's rugby sevens team helped to sandbag around the Uprising Beach Resort, near Taunovo Bay, as waves surged ashore.
James Pridgeon posted to Facebook: "Very lucky to have to Spanish Men's Rugby 7s team at the hotel to help restack what sandbags we can! Ocean is relentless!"
In Auckland, WeatherWatch analyst Philip Duncan has labelled it "the biggest and fiercest storm in the world right now".
Residents of Fiji's two main islands, Viti Levu and Vanua Levu, were warned to prepare for what could be the most powerful cyclone ever to pummel their country in its recorded history.
It's feared, however, that locals in the capital, Suva, on Viti Levu, may not be taking the warnings seriously enough, as the city has rarely experienced a really damaging storm.
Some predictions for the cyclone's path put it making landfall in Suva, or passing close by.
"Most of the people in Suva are under the misapprehension that Suva doesn't get cyclones, that it's only the north and the west of the country that seem to get them and the ones that come past Suva are weak and insipid," Fiji Met Service meteorologist Neville Koop told Australia's ABC News.
"This is the exception to that - it's probably one of the strongest cyclones to affect the capital in the last decade or two."
Mr Koop added: "The potential for devastation is high and there is a very real risk that people will lose their lives."
Aid agency Unicef said the cyclone was due to pass over Suva and "the risk of disaster for children and families is high".
At noon today local time (1pm NZT), Winston was about 30km east-south-east of Taveuni, or around 235km east-north-east of Suva, the Meteorological Service said.
"On this track, the cyclone is expected to be located about 270km west-north-west of Lakeba or about 130km north-north-east of Suva at 7pm [8pm NZT] today and about 415km west-north-west of Lakeba or about 140km north-west of Suva at 7am [8am NZT] tomorrow.
"Very destructive winds may begin several hours before the cyclone centre passes overhead or nearby."
At 4pm local time (5pm NZ time) Cyclone Winston was tracking to pass Fiji further north than first thought, which places it not only right amongst the most popular parts of country but it also keeps the cyclone in the highest category, Category 5.
Weather Watch said the storm has "staggeringly low" air pressure at 917hPa and it is still dropping meanwhile winds are averaging 230kmh and gusting to 325 to 350kmh or even higher, according to some models.
The weather service said there was a chance the storm could 'wobble' a bit from the predicted course - but the window for change has almost closed.
Bale Rokodi of Tuatua village on Koro Island said people remained in their houses and no one had moved to the evacuation centres provided by the National Disaster Management Office (NDMO).
The Fiji Times said there had also been reports of damage to farms in Kabara, Lau, from strong winds.
Filipe Jitoko, speaking to the newspaper from Lomati village, in Kabara, said strong winds had destroyed banana crops and newly planted cassava.
Villagers had been advised to stay indoors, he said.
Some were evacuated. Peace Corps volunteer Luigi Zeccardo said he and his colleague had already been flown from Koro island.
The weather turned bad very quickly as they were waiting for the plane to pick them up, he said.
Over the course of an hour, a thick blanket of fog came down, winds increased and it was almost impossible to see.
The plane had to make a couple of attempts to pick them up from the grass landing strip, which is on a slope, but they were now safely back in Suva, Mr Zeccardo said.
