Nearly half the population of Tuvalu have been severely affected by the devastation wrought by Cyclone Pam, Prime Minister Enele Sopoaga said Sunday, with other Pacific island nations also taking a hit.

While the focus has been on devastation in neighbouring Vanuatu, Tuvalu -- a grouping of nine coral atolls with a population of less than 11,000 -- is also struggling to cope, he told Radio New Zealand International.

"Forty five percent of the population of Tuvalu, most of whom are on the outer islands, have been affected, badly, severely affected," he said of the island chain some 1,550 kilometres (960 miles) northeast of Vanuatu.

"We are worried about the aftermath in terms of hygiene and supplies of essential materials like food, medicine and water."

Few details of the impact were given. But Sopoaga said most people living on the outer islands of the ex-British colony formerly known as the Ellice Islands had been affected, with houses and crops washed away.

He told the broadcaster there were health and safety concerns after cemeteries were destroyed and government boats were setting off later Sunday to assess the extent of the damage.

Aurelia Balpe, the Fiji-based head of delegation for the International Federation of Red Cross and Red Crescent Societies in the Pacific, said there had been extensive flooding in the low-lying nation.

"Tuvalu has had storm surges and up to six of its islands have been affected. People have spoken of four-to-five metre (13-16 foot) waves," she told AFP, adding that "people are hip-high in water".

"Some houses have fallen over and other infrastructure has been hit, with one hospital destroyed."

Balpe said other Pacific nations, including the Solomon Islands and Kiribati, had also been battered although not as badly as Vanuatu.

"Kiribati has also had storm surges," she said, with the main causeway on the islands badly damaged.

"There's basically one road on the islands and the bridge has been destroyed, which is seriously impacting transport."

On the Solomons several houses were razed with areas inundated by water, causing landslides.

"It is unprecedented in terms of the number of places impacted," Balpe said of the Pacific.

"But we have not heard of casualties in the Solomons, Kiribati and Tuvalu at the moment."

Australian Foreign Minister Julie Bishop said Canberra was responding to a request from Tuvalu, one of the world's smallest and most remote countries.

"Tuvalu has announced a state of emergency and we are responding to that request with basic supplies, water, sanitation, tents, blankets and food," she said in Perth.

"In the case of Fiji, Solomon Islands and Kiribati, we understand assessments are being made. The impact is not as great but we wait to hear."

Cyclone Pam smashed into impoverished Vanuatu on Friday night with a state of emergency declared as relief agencies desperately scrambled to get help amid reports entire villages were "blown away".

The official death toll stood at six on Sunday, although the United Nations had unconfirmed reports of 44 people killed in just one Vanuatu province.

Aid groups said the scale of the disaster would not be known until reports filter in from outlying islands.