Cyclone Winston is pounding parts of Fiji, as the eye of the storm travels between Viti Levu and Vanua Levu.
People living in low-lying areas have been told to move to higher ground and more than 200 evacuation centres have been activated.
Communication to some outer islands has been cut, Nadi Airport is closed and public transport has been cancelled.
Fiji's Prime Minister is reassuring citizens that the government is thoroughly prepared to deal with category five cyclone.
In a statement released today, Frank Bainimarama says "as a nation, we are facing an ordeal of the most grievous kind. We must stick together as a people and look after each other. Be alert and be prepared."
He says the nation cannot be complacent, and has urged people to finalise preparations to "survive this terrible event".
"And I am especially concerned that some people in urban areas of the country in particular do not appear to have heeded the warnings about the seriousness of the threat we face.
"I ask parents to be especially careful of the young and the elderly. Do not allow anyone to go outside during the storm itself. The threat of being hit by flying debris is extremely high," the statement reads.
He asks people to make sure they have adequate food and water, flashlights, candles and lanterns, in case the power supply is disrupted, and a battery-operated radio. The government has also announced a strict curfew.
"Let us all pray for our nation, ourselves and each other ask God's blessing for our beloved Fiji," he says.
Weather and climate consultative service NaDraki Weather says the cyclone is "probably the strongest tropical cyclone to impact Fiji in a decade".
Severe Tropical Cyclone Winston was located about 175km northeast of Suva at 1pm today.
It is moving west at about 25 km/h and is estimated to have average winds of 230 km/h and momentary gusts of 325 km/h.
At this stage, the cyclone is expected to be located about 100km west-northwest of Nadi at 1pm tomorrow.
A damaging heavy swell warning remains in force, and flooding is expected in low-lying coastal areas of Fiji. Heavy rain and squally thunderstorms are also expected.
The Land Transport Authority has advised all public transport to "cease movement at 5pm today for public safety reason". This includes buses, taxi, mini bus and carrier.
In a briefing with heads of department at the Disaster Management Centre (DISMAC) in Labasa this morning, the Commissioner Northern has directed all business operations to be called off as Cyclone Winston is expected to hit Vanua Levu from 3pm today.
DISMAC operation in the North Jovesa Vocea says the public advisory is "not a curfew but a proactive precautionary measure for members of the public in both municipalities."
For boaties, winds of hurricane force and phenomenal seas within 30 nautical miles of the centre are expected.
All vessels within 300 nautical miles of the centre are requested to send reports every three hours to RSMC Nadi.
Ola Fou is Tearfund's main partner in Fiji, and has capacity to manage an emergency response.
Ola Fou is preparing for the impact of the storm – its staff and students are spread across the main two Fiji islands, mostly in urban settlements.
Amani Waqetia, the manager of Ola Fou, a Fijian youth and community training programme, says it's important to inform people about a plan of action.
"At the moment within our organisation we are getting in touch with the most of our students and just informing them to make sure they are preparing their communities for this disaster that is coming,” he says.
Mr Waqetia, who is in Suva, says people are feeling intimidated, and preparing for the worst.
He says people are putting up shutters, tying down ropes and making sure food is well-stocked.
“Yesterday…I had to walk past quite a few supermarkets because I knew that I could not get a quick purchase because there were quite a number of people that were queuing up,” he says.
Mr Waqetia says there has been no major damage at the moment, although big gusts of wind are sweeping the area, and the skies are dark and cloudy.
He says the most damage is expected tomorrow morning, as the cyclone will fully hit this evening.
"Nobody wants to take these warnings lightly. From my point of view everyone is taking these warnings…very seriously. We can’t let this disaster get us by surprise."
He says people are storing batteries and making sure communication devices are ready for when power shuts off.
Fiji MetService says the cyclone is expected to be located about 100km north-northwest of Suva at 5am tomorrow.
A hurricane warning remains in force for Vanuabalavu, Yacata, Mago, Cicia, Tuvuca, Nayau, Koro, Gau, Vanuavatu, Taveuni, Qamea, Laucala, Ovalau, Wakaya and southern Vanua Levu.
A storm warning remains in force for Lakeba, Oneatu, Moce, Komo, Namuka, Ogea, Moala. The rest of Vanuau Levu and nearby smaller islands is also affected by this warning.
A gale warning remains in force for the rest of Fiji.
At 6am Vanua Balavu reported sustained winds from the south of 92 knots, or 175km/h, NaDraki Weather posted on social media today.
In a post to social media, the government warned members of the public to be on high alert and to make necessary preparations which include the fastening of walls and roofs, trimming branches, installing shutters to glass areas and preparing an emergency kit.
Although the eye of the cyclone is likely to pass north of Suva, weak structures in the capital are at risk in the strong winds.
NaDraki Weather says flooding of major rivers is almost certain in low-lying areas, with rain expected over the centre of Viti Levu tomorrow morning.
There is also risk that damage to the hydro-plant and power lines in Monasavu will cause disruption to electricity supply.
Yesterday the storm was upgraded from a category four to five following its departure from Tongan shores leaving at least 10 homes destroyed and 200 homes seriously damaged in its wake.
The slow-moving Cyclone Winston swept across the northern islands of Vava'u, the worst hit area, sending around 2500 people fleeing to evacuation centres.
Kiwis planning on heading to Fiji before Tuesday 23 are being urged by Air New Zealand to adjust or cancel their plans at no extra cost.
Fiji Airways flights within Fiji today have been cancelled. Some flights to Melbourne and Sydney have been advanced by hours and had an aircraft upgrade.
A departing and arriving Air New Zealand flight between Auckland and Nadi today will be operating as normal "subject to the increasing severity of Cyclone Winston".
A local tourist resort in Fiji's capital Suva told Newshub they are considering moving guests into upstairs rooms for safety reasons, and estimate around 10 percent of their bookings have been cancelled.
There is also a huge concern Cyclone Winston could exacerbate the Zika virus threat. Access to clean water, sanitation and food is critical.