Fiji's Met Service says Tropical Cyclone Tomas has intensified over night and has been upgraded to category four.
The Met Service says the storm is heading south towards the eastern edge of Vanua Levu with average wind speeds of 170 kilometres per hour.
A senior forecaster, Matt Boterhoven, says Cyclone Tomas is 185 kilometres northeast of Labasa, but winds are already being felt in the north of the second island of Vanua Levu.
He says over the next 18-24 hours the cyclone could reach average wind speeds of 205 kilometres per hour.
"Tropical Cyclone Tomas is moving on a southerly track around twelve kilometres per hour. At the moment it's causing heavy rains in the northern parts of the group near Vanua Levu and expect a lot of flooding on the northern main island near Cikobia. We expect some very disruptive hurricane force winds with average wind speeds of 165 kilometres per hour."
Matt Boterhoven says Cyclone Tomas is expected to pass eastern edge of Vanua Levu this evening.