Vanuatu urgently needs food and relief supplies, officials said, days after Cyclone Pam caused massive devastation across the Pacific nation.

Houses, schools and crops have been destroyed by the storm, which hit the islands as a category five.

Eleven people have died, the UN said, revising down an earlier toll of 24.

But this could rise. There are islands south of Port Vila where the situation is not yet known. Those who have flown over them report widespread damage.

Teams had managed to land on Tanna and Erromango islands - both directly in the path of the storm - on Tuesday afternoon local time, the Associated Press reported, citing an aid agency.

Military planes that have flown over the islands have reported extensive destruction to houses and crops.

"We understand that the reconnaissance imagery shows widespread devastation," Australian Foreign Minister Julie Bishop said of Tanna. "Not only buildings flattened - palm plantations, trees. It's quite a devastating sight."

The storm hit Vanuatu on Saturday, bringing very high winds.

Across the nation, many people have lost their homes or face extensive rebuilding. Telecommunications, power and water supplies have all been badly affected.

"We urgently need water purification tablets to make sure that the water is safe to drink," Alice Clements of Unicef told the BBC.

"We urgently need food for communities whose crops have been absolutely destroyed and will take up to three months to grow. We absolutely need shelter."

Benjamin Shing, of President Baldwin Lonsdale's office, echoed her comments.

"We are relying on the fact that the food crops and the gardens are still edible and they can be used for the first week but after [that] we'll need to get some rations on the ground," he told Australian media.

As well as crops, residents' stockpiles of food had been destroyed and wood was too wet for people to cook with, reports said.

Aid is arriving from nations including Australia, New Zealand and the UK but officials say distributing supplies will take time, given damage to infrastructure and the number of islands.

In Port Vila, the capital, a clean-up is under way but the destruction was extensive. Power and water have been restored in some areas but up to 90% of homes have been damaged.

The hospital is coping with an influx of injured people but a surgeon said beds had been moved outside because of structural damage.

On the main island and in the provinces of Torba and Penama to the north, some 3,300 people were in evacuation shelters, the UN Office for the Coordination of Humanitarian Affairs said.

The president, returning from a conference in Japan, has described the storm as a "monster" that wiped out years of development.

He has linked the disaster to climate change, citing changing weather patterns, rising seas and heavier-than-average rain in Vanuatu.

Australia announced on Tuesday that it was sending more personnel, including a search and rescue team, and three more military planes carrying aid.

BBC