Two people have died while more than 2,000 others remain in evacuation centres as Tropical Cyclone Sarai moves through Fiji's south-east.

Key points: The two casualties were reportedly in floodwaters prior to their death

The two casualties were reportedly in floodwaters prior to their death Winds up to up 110 kph are forecast to hit Fiji's southern island groups on Sunday

Winds up to up 110 kph are forecast to hit Fiji's southern island groups on Sunday The cyclone is forecast to strike Tonga's northern islands by New Year's Day

Vasiti Soko, director of Fiji's National Disaster Management Office (NDMO), told reporters on Saturday that an 18-year-old student drowned after being swept away by strong currents while swimming in waters on the southern island of Kadavu.

In an NDMO update at 5:30pm Sunday (local time), Ms Soko confirmed that the body of a man in his 40s was found by villagers in Naitasiri province, on Fiji's main island Viti Levu.

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A tweet from the office also confirmed that a 15-year-old boy, who was hospitalised in a critical condition after being reportedly being struck by a falling roof, "is recovering well" at the Colonial War Memorial Hospital in Suva.

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The last update from the NDMO said 2,001 people were in 54 evacuation centres across the country.

The cyclone did not make landfall as it moved south-eastward around Viti Levu, but its proximity to Fiji sent strong winds and rain hurling across the Pacific nation.

In the south, islands such as Kadavu, Vatulete and Matuku were met with winds with average speeds of up to 110 kilometres per hour, with momentary gusts of 150 kph, according to the Fiji Meteorological Service.

The NDMO's last update said there was damage to Kavadu, but it was not able to confirm the full extent as its officers were in the process of gathering information.

As of Sunday evening, the cyclone has moved past the majority of Fiji's islands, with its centre forecast to be 70km north-west of Ono-i-Lau in the country's south-east by Monday morning (local time).

The Met Service continues to update local conditions across Fiji via its Facebook page.

Cyclone expected to hit Tonga on New Year's Day

Tropical Cyclone Sarai is expected to downgrade to a category one storm as it moves into Tongan waters. ( Facebook: Tonga Meteorological Service )

Tropical Cyclone Sarai is expected to leave Fiji's area of responsibility by New Year's Day, moving into Tongan waters on Wednesday.

The last forecast map from Tonga's Meteorological Service predicts Sarai move between the kingdom's northern Vava'u and Ha'aapi island groups by Thursday morning.

The service has issued a tropical cyclone alert which carries a strong wind, rain and flash flood alert for all Tongan land areas.

Meteorologist Neville Koop, who is based in Fiji's capital Suva, told the ABC on Saturday that the Fijian islands remaining in the cyclone's path were much more vulnerable to disasters because of their remoteness.

"They're much more difficult for us to access and to take supplies and assistance to if they get severely affected …," Mr Koop said.

However, officials such as the Red Cross's Ellie van Baaren told the ABC that many Fijians were well prepared.

"There's a huge amount of information that was delivered before Sarai [was] named as a cyclone," she said.

"People knew that it was heading this way that it could potentially be a cyclone. And about 2,000 people … were reported to be in evacuation centres as a precautionary measure."

Fiji looking to assess damage as PM visits affected areas

Mr Bainimarama (right) visited people whose homes were damaged by the cyclone on Sunday. ( Facebook: Fijian Government )

On Sunday Fiji's Prime Minister Frank Bainimarama met with cyclone evacuees at a primary school north-east of Suva in Vunivivi.

The PM also toured damaged homes and was briefed by local health officials on the situation.

A post from the Fijian Government Facebook page reported that residents were informed that the Government was "looking into" cyclone assistance.

The NDMO's Ms Soko said those remaining in the centres are due to receive food rations.

Medical teams also continued to carry out measles vaccinations.

Flights restored, but people urged to avoid flooded roads

Heavy rains and wind are raising the risk of land slips and flooded roads. ( Twitter: Fiji Roads Authority )

As the cyclone moved across Fiji, numerous roads and crossings were flooded or blocked as a result of fallen trees.

Ms Soko urged people to avoid driving through flooded roads of unknown depths, as some may continue to be hazardous with strong currents.

Videos and images posted on social media of the cyclone's effects showed seawater inundation to coastal areas, along with various flooding events due to heavy rainfall.

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The Fiji Times also reported that a vehicle convoy carrying six people and a cow was washed away in floodwaters.

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Several flights, ferry and bus services were also cancelled as the cyclone moved across the islands.

By Sunday, most of Fiji Airways and Fiji Link flights were restored except for services to and from Kavadu Island.