TANNA, Vanuatu (REUTERS) - The people of the southern Vanuatu island of Tanna are used to ferocious storms, but even here, few were prepared for the awesome force of Cyclone Pam.

Teacher Saimoni Nainoca survived the cyclone's gusts of more than 300kmh by huddling with a friend in his home, although part of the roof was ripped off about midnight last Friday.

Four days later, the South Pacific island's airport has only just reopened, while communications and power remain down. "We never thought the storm was going to be as bad as it was. This was a roaring and damaging cyclone," Nainoca, 70, said as he sat in the shade of a damaged shop near the waterfront of the town of Tanna. "The roof was rattling like a machine-gun. It was like a battlefield." When he emerged in the morning, he couldn't believe the scale of the destruction, he said.

The category 5 storm snapped huge trees in half, ripped open corrugated metal roofs like tin cans and flattened traditional thatched houses in villages outside the town of 29,000 people.

Many buildings in the town, about 200km south of the capital, Port Vila, were extensively damaged, but the absence of a major storm surge meant most large structures survived.

The official death toll from the cyclone was 11 across Vanuatu, the U.N. said, but the figure could rise.

On Tanna, the toll stands at five, including two women killed when a wall collapsed as they sheltered in a church. Relief agencies fear the number could rise significantly as news trickles in from settlements restoring communications links. "What we need right now is water and shelter," said Nainoca, a teacher at Tanna's Tafea College. "The food in the shops will run out in a week. We need international support and we need communications to be restored." About 50 people who took shelter in Loukatai Primary School, located between the airport and the town, were still there on Tuesday, unable to return to their destroyed homes. "We'll have to teach the children under the trees until these people can go back home, which could be a month or two,"said the headmistress, Mary Korisa.

Amid the destruction, laughing children played and scavenged in the wrecked forests with slingshots and machetes.

International aid, including food, water and building materials is arriving in Port Vila, and should get to Tanna and other hard-hit islands within days, relief workers said.

Helicopters were set to begin fanning out from the capital to visit isolated communities out of touch since the storm. "We are miles away from anywhere here and communications are down. People are going to need everything, from shelter to blankets and kitchen sets," said Daniel Dieckhaus, an adviser with USAid.

Despite the storm's surprising ferocity, the government's early warnings helped people survive, Nainoca said. "I think we were a bit lucky and people had planned where to run and find shelter if their houses blew down."