Cyclone Tomas is expected to bring winds of more than two hundred kilometres an hour to the two main islands of Fiji from Monday morning.
The cyclone is currently north north west of Futuna and moving southwest at five knots.
Winds of up to 60 knots are forecast for Futuna and Wallis with heavy rain and flooding, but easing from the morning.
Tuvalu is also experiencing winds of this intensity.
The Fiji Metservice says Tomas is a category two system but is likely to significantly intensify over the next day or so.
Forecaster Alipate Waqaicelua says by then the cyclone could threaten Vanua Levu and Viti Levu with winds of up to 125 knots.
"At the moment all the model guidance is agreeing to bring the track right across Fiji, starting from Vanua Levu, the big island to the north, and then come down through Fiji on its way southward."
Meanwhile, Tropical Cyclone Ului has now moved to the northwest away from Vanuatu's northern islands.