One person is confirmed to have died in Papua New Guinea and widespread casualties are feared after a powerful typhoon battered Vanuatu overnight.
Cyclone Pam triggered flash floods in the isolated Pacific island nation, with winds up to 167mph hitting the Vanuatu islands.
The category five storm named Cyclone Pam, struck the South Pacific archipelago, where more than 267,000 residents live on 65 of its islands.
The storm had moved off its expected track, changing course and putting populated areas directly in its path. The eye of the cyclone was expected close to the central island of Efate, home to the capital Port Vila, where 47,000 people are residing.
The Vanuatu Meteorological Services warned of "very destructive winds and very rough to phenomenal seas with heavy swells".
David Gibson, acting director at the Vanuatu Meteorological Services, said: "As far as I can remember, this is the first Category Five cyclone to come very close to Vanuatu. This is obviously a once-in-a-lifetime experience for most of us."
Authorities have issued red alerts across Vanuatu, warning residents to take shelter in the face of potential flooding and landslides.
Sune Gudnitz, the regional head of the U.N. Office for the Coordination of Humanitarian Affairs, said: "We fear the worst. Vanuatu is a very vulnerable place because of its location in the middle of the ocean. It is possible that there will be a death toll that could be high. I can't give any numbers. I think it is a well-grounded fear."
speaking from Fiji.Many Vanuatuans are ill-equipped to cope with such a storm, living in accommodation which would be unable to withstand such an onslaught.
UNICEF's Alice Clements, in Vanuatu, said: "Everybody is concerned about shelter, ensuring that the shelters are going to be strong enough for them."
Clements said the cyclone would "behave pretty much like a tsunami" wreaking devastation in its wake.
The cyclone has already destroyed homes on other Pacific islands including the Solomon Islands and low-lying Kiribati where there are reports of significant flooding.
The impact of the cyclone could be felt as far away New Zealand.