The Fiji Red Cross says Tropical Cyclone Evan is different from previous storms because of the way it is affecting the whole of Fiji.
The cyclone is moving southwest at about 18 kilometres per hour, with winds of up to 270 kilometres per hour at its centre, which is just off the west coast of Viti Levu.
Almost 4,000 people are in evacuation centres in the northern division, where weather conditions are now easing and the authorities are preparing to carry out an assessment of the damage.
The Red Cross's director general Filipe Nainoca says it has five supply centres there and seven in the west but supplies will run low in the short term.
"Because of the extent of the reach of the cyclone but we're hoping to be able to reach the most vulnerable families as quickly as possible and with what we have and then work backwards from there."
Filipe Nainoca says Fiji has always had good support from its neighbours and from Australia and New Zealand.