The south pacific nation Fiji, is being severely battered by Cyclone Evan, as thousands of people have been forced to flee to evacuation centres.

Cyclone Evan pummelled the main island Viti Levu on Monday with winds exceeding 200 kilometres per hour, bringing down trees, blocking roads and forcing all flights to be grounded at the popular tourist destination.

Fijian authorities have confirmed there has been no reported casualties from the category four storm, unlike in neighbouring Samoa, where it killed at least four people late last week and left another 10 missing.

Government spokeswoman Sharon Smith-Johns, who earlier on Monday told Fijians to "prepare for the worst", said emergency planning appeared to have paid off, including moving hundreds of tourists from luxury resorts on outlying islands.

She said some 3,500 people were sheltering in well-stocked evacuation centres, locals appeared to be heeding warnings to avoid travel and all non-essential government personnel had been ordered to remain at home.

"We've had a week to prepare for this, so we're as prepared as you can be," she told Radio New Zealand.

Smith-Johns said that while the lack of early casualties was "encouraging", the cyclone would continue to batter the west coast of Viti Levu overnight and there was no room for complacency.

"The extent of the damage I don't think we're going to know until tomorrow morning when we wake up and see how badly it has hit," she said.

The Joint Typhoon Warning Centre said Evan could generate 12 metre swells, creating a major flooding concern for authorities.

The cyclone is thought to be the strongest to threaten Fiji since Cyclone Kina, which killed 23 people and left thousands homeless in 1993.