The Fiji Disaster Office says Vanua Levu is reported to be suffering extensive damage as the force of tropical cyclone Ami has hit the area, with two people feared killed.
The country's northern division has been affected by very destructive winds and heavy rain.
A hurricane warning is in force for some smaller islands in Fiji's east as cyclone Ami is moving towards Tonga.
The disaster management officer Waqa Varea says the communication lines to Vanua Levu have been cut, and there is no power.
She says about 120-thousand people live in the area, and while they know the damage is extensive they have only one report of possible casualties.
"There was a young boy and a young girl who escaped from their home because it was blown away by the cyclone and they raced towards a nearby church and just when they got there the church also collapsed on them."
Fiji's capital, Suva, woke up this morning to severe storm conditions with wind and rain.
Parts of Nausori town, to the north of Suva, are being evacuated this morning as the Rewa River threatens to flood.