Humanitarian aid began pouring into Fiji Tuesday, as the death toll from super-cyclone Winston rose to 29 and officials warned the devastated Pacific nation's recovery could take months.

With authorities still struggling to grasp the scale of the disaster on remote island communities, Australian and New Zealand planes arrived with desperately needed supplies of food, water and medicine.

Government spokesman Ewan Perrin said the news was grim from the few isolated villages which had managed to restore communications after the storm hit last weekend.

"The official death toll now is 29, another eight bodies were found on the island of Koro since yesterday," Perrin told Radio New Zealand in a phone interview.

"We are expecting it to rise but we're hoping it's going to rise by a very small number."

Severe tropical cyclone Winston, the most powerful storm ever recorded in the southern hemisphere, lashed Fiji with wind gusts of 325 kilometres (202 miles) per hour, leaving a trail of destruction.

More than 8,000 people are still sheltering in evacuation centres and Perrin said some villages had hardly any buildings left standing.

"We're still trying to get people on the ground in these areas to do a detailed assessment of the damage. We're just taking it day-by day," he said.

"In some places people are going to be displaced for months because they've lost everything."

Perrin said 2,000 families were homeless on Koro alone and two ships were steaming to the island with relief supplies.

"We haven't been able to make contact with all parts of Fiji, although with the assistance of the New Zealand Air Force we've managed to do aerial inspections across almost all of the islands," he added.

The aerial photographs show entire villages flattened, with homes reduced to piles of kindling and roofing strewn about.

On one battered island, a large steel-hulled ship sits high on a beach after being driven ashore in huge swells.

- Secondary disaster fears -

"The images emerging from early aerial assessments of affected areas are truly heartbreaking, leaving little doubt about the ferocity of this cyclone," said the UN's Fiji coordinator Osnat Lubrani.

"It is clear from these catastrophic impacts that Fiji is facing a long road to recovery."

The nation has declared a month-long state of natural disaster after a storm that Prime Minister Voreqe Bainimarama described as an "assault on Fiji".

Power is gradually being restored in the main centres and roads cleared of felled trees.

The international airport at Nadi has also reopened, allowing international tourists caught up in the disaster to leave.

Aid efforts have ramped up, with Australia contributing Aus$5.0 million (US$3.6 million) and New Zealand NZ$2.2 million (US$1.5 million).

India pledged US$1.0 million and the European Union dispatched a disaster management expert to assess its best response.

Wellington has mobilised two military aircraft, while Canberra is sending two planes and four helicopters, as well as specialised medivac teams.

UN aid chief Stephen O'Brien said hundreds of thousands of Fijians had been affected.

"We must do all we can to help people rebuild their lives and livelihoods," he said in a statement from New York.

Aid agencies such as the Red Cross, Oxfam, Care Australia and Save the Children are on the ground distributing supplies and providing expertise on issues such as sanitation in evacuation centres.

"Clean water will be vital to prevent the risk of a secondary disaster rearing its head in the days and weeks following Tropical Cyclone Winston," Oxfam's Jennifer Worthington said.

Care Australia coordinator Sarah Boxall said disease could spread quickly in crowded shelters.

"In this type of emergency, it really is a race against time to get immediate relief to those who have lost everything and ensure families can stay safe and healthy," she said.

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VIRGIN AUSTRALIA HOLDINGS