Tens of thousands of people in Vanuatu are still facing critical food and water shortages a month after Cyclone Pam hit, aid agencies say.

The category five cyclone that struck Vanuatu and neighbouring islands was one of the worst in living memory for the Pacific region, destroying many homes, schools and an estimated 90 per cent of crops.

While emergency relief has flowed to those in need, many people face longer-term problems.

The United Nations estimates 100,000 people do not have access to safe drinking water, while the World Food Program said almost 60,000 people do not have sufficient food.

Most of the population depends on subsistence agriculture and aid agencies said it could take up to a year for communities to become self-sufficient again.

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"A lot of food rations that have been distributed have practically reached all the people," government spokesman Kiery Manassah said.

Mr Manassah recently visited the southern island of Tanna, one of the hardest hit, and found the root vegetables that are a staple in the local diet have largely survived.

"So a lot of people there would be able to survive with the food rations that are being distributed," he said.

"I managed to speak to a lot of people there, they seem to have ... for example the yams are still intact.

"But for the outer islands for example, the Shefa, those islands are quite small and so they would probably need a lot more attention in terms of food rations."

The UN said a further $20 million is needed to help Vanuatu recover.

Housing is another concern with the UN estimating 6,000 people are still living in temporary shelters.

Many of the leaves and timber used for traditional thatches and house building were destroyed a month ago, and Mr Manassah appealed to the international community to send more permanent emergency shelters.

"Send some tarpaulins, they were useful, but not so useful in the longer term," he said.

"And so we are, I think the prime minister has asked for more support in that regard in terms of more tents coming in to help people so they could probably establish themselves."

Fear for the future of Vanuatu's children

The hardships are particularly tough for Vanuatu's children, said the Vanuatu country director for Save the Children, Tom Skirrow.

Schools have been slow to recover after being damaged when Cyclone Pam hit. ( Reuters: Edgar Su )

"The children are always the most vulnerable in these sorts of circumstances, parents are trying to rebuild their homes and children are left alone," he said.

"There's a lot of areas where [school] buildings have been destroyed.

"I mean obviously with the food and water needs, children are more susceptible to disease, such as diarrhoea when water isn't clean.

"So I'm quite worried personally about their futures."

Mr Skirrow said international help was making a difference, but said Vanuatu must not drop off the radar.

"I think what's worrying me slightly is that international assistance will close down and somewhat stop," he said.

"Obviously everything is being coordinated with the Vanuatu government but the needs of the people and the children and trying to get back to a life that [they] knew four, five weeks ago, in terms of their supply of food, supply of water, their housing, their public institutions like hospitals - so much of this has been just completely wiped out."

Mr Manassah said less than half of the money pledged at the time of the cyclone had actually been received by the country's finance ministry.

"The government is hoping that those countries that pledged to give assistance will honour those pledges," he said.

Tuvalu also still rebuilding from Cyclone Pam

Meanwhile, in the neighbouring island nation of Tuvalu aid agencies are still assisting with Cyclone Pam recovery efforts.

The Red Cross and other aid agencies have sent a ship filled with volunteers and emergency supplies to Tuvalu's northern islands.

Massive tides caused by the cyclone caused severe damage to the low-lying islands.

A volunteer aboard the ship, Rosemarie North, said huge waves also hit a coastal graveyard.

"It sent human remains, bones, up and down the coast and through people's homes, actually, onto the roads," she said.

"What it's done is left them really nervous about going fishing or eating any poultry or pigs or anything they think might have come close to those human bones."