The Vanuatu Meteorology and Geo-Hazards Department said Tropical Cyclone Harold is moving in a south-easterly direction at 8kmh.
The system is gathering more strength as it moves slowly towards northern Vanuatu.
The Fiji Meteorological latest forecast tracking map indicates Tropical Cyclone Harold will be a powerful category 5 when it crosses over Vanuatu.
A category five cyclone can have sustained winds of 252km/h.
The Vanuatu National Disaster Management Office said the provinces of Torba, Sanma, Penama and Malampa are now on Red Alert.