Tropical Cyclone Funa is crossing central Vanuatu with storm force winds.
The system has winds rising to 135 kilometres an hour as it moves from Santo eastwards past the island of Ambae.
The cyclone is moving at about 20 kilomeres an hour and is set to curve into a southeasterly direction as begins to move away from Vanuatu.
The Met Office says the sea is very rough in the affected areas with heavy swells.
People, including sea going vessels are strongly advised not to go out to sea until the system moves out of the area.
Heavy rainfall and flooding, including coastal flooding is expected in the affected areas.