Vanuatu's President Baldwin Lonsdale

Vanuatu's President Baldwin Lonsdale has called for international help after Cyclone Pam ripped through the Pacific archipelago.

Describing it as a "calamity", he said he spoke with a "heavy heart".

Aid agencies say the cyclone, which veered off its expected course today and struck populated areas has caused "complete devastation".

Save the Children says eight people are confirmed dead but it is feared dozens more may have been killed.

Unconfirmed reports said 44 people had died in Penama province in the north-east of Vanuatu, the UN's Office for the Co-ordination for Humanitarian Assistance (UNOCHA) said earlier in a statement.

Many residents are spending a second night in emergency shelters after finding their homes destroyed.

Lonsdale was speaking in Japan at the UN's World Conference on Disaster Risk and Reduction.

"I stand to appeal on behalf of the government and the people of Vanuatu that the global community give a lending hand in responding to these very current calamities...that have struck us," he said.

Save the Children's Vanuatu Country Director Tom Skirrow said today, "The scene here this morning is complete devastation - houses are destroyed, trees are down, roads are blocked and people are wandering the streets looking for help.

"Communications are down across much of the country with the total extent of the devastation unlikely to be known for several days."

Pam brought winds of up to 270km/h and torrential rain.

'Entire villages destroyed'

Chloe Morrison, an emergency communications officer with World Vision who is in the capital, Port Vila, today said the streets were littered with roofing, uprooted trees and toppled power lines.

She said there were reports of entire villages in remote areas being destroyed.

"The damage is quite extensive in Port Vila but there are so many more vulnerable islands. I can't even imagine what it's like in those vulnerable communities.''

A priority was to make sure residents had shelter and enough food and drinking water.

Unicef spokeswoman Alice Clements described the cyclone as "15-30 minutes of absolute terror" as it passed over Port Vila.

"I saw the sliding doors from my three-storey-hotel room completely blow away - it was terrifying," she said.

Unicef in New Zealand warned that Cyclone Pam could be one of the worst ever weather disasters for the region.

"While it is too early to say for certain, early reports are indicating that this weather disaster could potentially be one of the worst in Pacific history," New Zealand Executive Director Vivien Maidaborn said in a statement.

Australia says it is preparing to send a crisis response team to Vanuatu if needed.

Although thousands of people spent the night in emergency shelters, many more were forced to ride out the storm in their own homes.

All six provinces of Vanuatu were under red alert, meaning people are advised to immediately seek shelter.

Located about a quarter of the way from Australia to Hawaii, Vanuatu has a population of 267,000 spread over 65 islands. About 47,000 people live in Port Vila.

Pam, a category five tropical storm, had already caused major damage on other Pacific islands, including Kiribati and the Solomon Islands.

Tuvalu, a group of nine tiny islands north-east of Vanuatu, has also declared a state of emergency after the cyclone caused flash floods there.