PORT VILA – A category five storm has killed at least ten people in Vanuatu in one of the strongest-ever tropical cyclones to have hit the South Pacific.

There are also unconfirmed reports that more than 40 people may have perished on remote islands.

The official death toll in Port Vila stands at six, with two on Tanna Island and another 20 confirmed injured, according to Vanuatu’s National Disaster Management Office.

Vanuatu coordinator of climate change not-for-profit organisation 350, Isso Nihmei, said he and others tried to rescue three people in Port Vila who later died in hospital.

“We heard some of the people who were living close. They were shouting and calling us. So once we went down there, we saw this guy who was already dead,” he said.

“There were other people on the other side, so we went down to rescue them but they were really weak. We got them to hospital but they died in half an hour.”

Nihmei said they had injuries to their faces and bodies and were living close to the sea. He said they had chosen to stay because of their boats.

Power and communications are down across much of the country which has made it difficult for authorities to confirm damage and a death toll.

Two Australian military aircraft, including one with medical experts, search and rescue teams and emergency supplies, touched down in the capital on Sunday.

A New Zealand Hercules aircraft carrying eight tonnes of supplies and an initial team also landed on Sunday at Port Vila’s airport, which has been partially reopened.

Humanitarian organisations have warned of “complete annihilation” in Port Vila, where the cyclone reportedly tore through at 340 kilometres per hour.

But some fear the devastation could be even worse in the outer islands.

The United Nations Office for the Coordination of Humanitarian Affairs said there were no official reports of deaths or injuries, but there was an unconfirmed report that 44 people died in the central Penama province. As of Monday morning local time this report remained unconfirmed.

Residents of Port Vila spent the night bunkering down as the terrifying storm raged, waking to find trees had been uprooted, homes destroyed and areas flooded.

Tom Skirrow from Australia’s largest aid agency Save the Children said the scale of devastation across the country is starting to become clear with estimates up to 10,000 people needing emergency accommodation in the capital.

Save the Children’s Head of Humanitarian Affairs, Nichola Krey, said the storm was as severe as feared.

“It hit Port Vila at an incredible 340 kilometres an hour,” she said. “Some reports are saying it was at that speed, so you can imagine the flimsy housing in Vanuatu made of corrugated iron and very weak wood.

“You can imagine what 340 kilometres an hour wind does to that.”

CARE Vanuatu program manager Charlie Damon said she had also received unofficial reports of fatalities.

Damon, speaking from Port Vila, said most roads were blocked by fallen trees and it was still quite dangerous to go outside.

She said even evacuation centres were damaged.

“Some have been flooded and some evacuation centres have also lost parts of their roofs too, but those on the outer islands certainly will be feeling the brunt of this as they just don’t have the facilities as we do in Port Vila,” she said.

The Vanuatu Meteorological Services said very destructive hurricane-force winds of 250 kilometres per hour continued to affect the country’s southern provinces. It said the central pressure of the system was estimated at 900 hectopascals, which is among the strongest tropical cyclones on record.

Aid agencies were scrambling for information and preparing to send teams to Vanuatu – with a UN disaster assessment and coordination team expected to arrive later today.

“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,” Unicef New Zealand’s executive director Vivien Maidaborn said in a statement.

“The sheer force of the storm combined with communities just not set up to withstand it, could have devastating results for thousands across the region.”

Aurelia Balpe, head of the Pacific regional office of the International Federation of Red Cross and Red Crescent Societies (IFRC), said there were unconfirmed reports of casualties in the capital Port Vila.

But they had greater fears for outlying southern islands, home to more than 33,000 people, where communication had been cut.

Morrison said communications have been so problematic that her aid group hasn’t yet been able to account for many of its own 76 staff on the islands and authorities have been unable to assess the extent of the damage.

UN Secretary-general Ban Ki-moon said the impact and scope of the disaster caused by Cyclone Pam wasn’t yet clear, but he feared the damage and destruction could be widespread.

“We hope the loss of life will be minimal,” he said during a World Conference on Disaster Risk and Reduction in Japan. The UN said it was preparing to deploy emergency rapid response units.

New Zealand has pledged one million New Zealand dollars to help with relief efforts. Australia was preparing to send a crisis response team to Vanuatu if needed, Australian Foreign Minister Julie Bishop said.

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 the capital.

The small island nation has repeatedly warned it is already suffering devastating effects from climate change with the island’s coastal areas being washed away, forcing resettlement to higher ground and smaller yields on traditional crops.

Scientists say it’s impossible to attribute single weather events like Cyclone Pam to climate change.