Tropical Cyclone Mal has intensified into a category 3 system but it is now showing signs of weakening, the Fiji Meteorological Service says.
It said the cyclone was moving in a south-southeast direction, closer to the Fiji Group, at about 23km/h.
On its current projected path, the Yasawa and Mamanuca Groups, western and southern Viti Levu, Vatulele, Kadavu and nearby smaller islands were at greatest risk of getting gale to storm force winds, the Fiji Meteorological Service.
Power outages were reported in Nadi, and local media had reports of heavy rain in parts of the Western Division.
There were eight active evacuation centres with almost 300 people taking shelter by Tuesday evening local time.
At 5am local time on Wednesday, Mal was about 155km southwest of Nadi and was showing signs of weakening within the following few hours, Fiji Metservice said.
"This indicates that the system has passed Nadi and its now moving close to Kadavu. It is currently moving southeast at a speed of 17 knots or 31km/hr," it said.
"While the winds should gradually ease over the Yasawa and Mamanuca Groups and western Viti Levu, gales force winds may continue to be experienced for few more hours.
"The risk of storm to gale force winds are still maintained for Vatulele, Kadavu and nearby smaller islands. Current analysis indicates that the destructive hurricane force winds associated with the system is confined close to the centre. So the chance of hurricane force winds affecting land areas is low.
The meteorological office said several parts of Fiji have received significant rainfall in the past 12 hours.
"Further rainfall will increase the risk of flooding in low laying and flood prone areas."
Forecaster Samisoni Waqavakatoga said the cyclone was expected to continue to weaken further as it continued tracking south southeast.
"It will stay in open seas and will rapidly weaken."
He said the worst conditions were expected over the western division, with gale and storm force winds.
Waqavakatoga said gusts in the most affected areas were expected to reach 157km/h and average winds would have been between 67km/h to 111km/h.
At one site on Viti Levu island more than 20mm of rain was recorded between 3am to 4am local time on Wednesday.