The Vanuatu Meteorology and Geo-Hazards Department said Tropical Cyclone Harold is moving in a south-easterly direction at 8km/h.
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.
The province of Shefa is now on Yellow Alert.
Red Alert, the highest alert level for a cyclone in Vanuatu.
When a RED ALERT is issued, you need to stay in a safe shelter
Stay tuned and informed through Radio, TV, SMS, or Internet
Turn off all gas and electricity and unplug all electrical items from the sockets
Stay in the strongest and safest part of your house or the evacuation centre and do not go outside
Stay away from doors and windows and keep them closed and locked
Remain indoors or in safe place and continue to listen to the radio and do not go outside until NDMO (Disaster Management Office) issues the 'ALL CLEAR' after the VMGD cancels the cyclone warning for your area.
Take care to avoid dangers caused by fallen powerlines, trees, damaged building and other debris
Support your family and neighbours especially the most vulnerable in your community.
A State of Emergency was declared by Vanuatu's President on 26 March in response to the Covid-19 pandemic.
The approach of Tropical Cyclone Harold may see a change to the government's state of emergency as people start to prepare for the category 4 cyclone.
In 2015, Tropical Cyclone Pam, a category 5 storm, devastated the Vanuatu group.