The Fiji Meteorological Service said tropical cyclone Mal is a category one system.
Schools in Fiji are closed on Tuesday, and Wednesday local time, and all public servants have been instructed to work from home.
Fiji's Metservice said at 3am local time, Mal was positioned about 450km West of Rotuma - Fiji's northern most island - and about 720km north west of Nadi.
It's moving south, south eastward at about 28kmph.
Forecaster Samisoni Waqavakatoga said on it's current track, the eye of the cyclone will get closest to Fiji at 3am Wednesday morning and be 170km west of Nadi.
"It is still a category one but there are high chances the environment is favourable for Mal to intensify further into a category two system within the next 6 to 12 hours before heading into Fiji waters," Waqavakatoga said.
"It's expected to reach a high end of category two [cyclone] while it makes its south eastward movement west of the Fiji group in the next 24 to 48 hours."
Waqavakatoga said there was a possibility it could reach category three status, with average wind speeds between 119kmph to 157kmph.