Severe tropical cyclone Kevin was just over Vanuatu's capital Port Vila on Saturday morning, bringing destructive winds and heavy rainfall.
The Fiji Meteorology Service says the huge weather system is moving south-east at 24km/h. It says it will be more than 12 hours before it leaves the Vanuatu group of islands.
Its winds are estimated at 165km/h, gusting up to 230km/h.
On Friday night the Vanuatu Meteorology Service upgraded the tropical cyclone to a category 4 before its power went out.
There have been reports of power outages in the capital even before the cyclone had reached it.
This is the second severe cyclone the country has been slammed with this week.
A state of emergency has been declared for areas of Vanuatu impacted most by severe Tropical Cyclone Judy which flattened properties before Kevin settled in.
Judy near Fiji
Cyclone Judy, which had caused significant damage to parts of Vanuatu before Kevin set in, is now to the far south of Fiji.
The Fiji Meteorology Service has issued heavy rain alerts across parts of the Fiji group. It says the associated rain bands and strong winds continue to affect the country.
The possible impacts from the system are likely to be flash flooding in low-lying areas.
UNICEF Vanuatu reports there has been damage to schools and to the country's Central Hospital.
Chief of Vanuatu's UNICEF field office Eric Durpaire said the government has reported about half the population has been affected.
Durpaire said the damage will have a medium- to long-term impact on the country.
Durpaire said children may not be able to go to school and it could be challenging for women giving birth.
Help from Australia, New Zealand
The Australian Government will deploy a rapid assessment team to survey cyclone damage at the request of the Government of Vanuatu.
A 12-person team and an initial assistance package will be transported to Vanuatu on a Royal Australian Air Force aircraft as soon as weather conditions allow.
RAAF aircraft will also assist the Government of Vanuatu with aerial damage assessments.
The Australian Government says it is working closely with partners such as New Zealand and France to support the Pacific nation's response.
RNZ
