The tropical depression east of Solomon Islands intensified into a tropical cyclone early Tuesday morning local time, the Fiji Meteorological Service says.
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.
On Monday, local time, the Fiji National Disaster Management Office reported several bridges and crossings were inaccessible.
The office called on the public to stay away and avoid crossing flooded roads, rivers, bridges, crossings, or walkways.
The Fiji Roads Authority had warned that the "heavy rain can lead to fallen trees, obstructing roads and footpaths" and is calling on people to "please stay vigilant".
Fiji's Agriculture Ministry is advising farmers in flood-prone areas to relocate to higher ground following the tropical cyclone warning.
Fiji weather office said a storm alert is in place for the Yasawa and Mamanuca Group, western, northern, and southern Viti Levu, Vatulele, Kadavu, and nearby smaller islands.
Rotuma, the western half of Vanua Levu (Dreketi, Bua to Savusavu), eastern Viti Levu, and Lomaiviti Group are under a gale alert.
Farmers within the identified areas are advised to take precautionary measures to mitigate potential damage to crops and livestock.