The United Nations on Tuesday launched an urgent appeal for nearly $30 million to provide life-saving assistance in Vanuatu after the island nation was ravaged by cyclone Pam.

The UN's humanitarian organisation said it had launched a flash appeal for $29.9 million to help 166,000 people in the Pacific archipelago after it was hit by the cyclone on March 13.

"That is more than half of the population of this island nation," OCHA spokesman Jens Laerke told reporters in Geneva.

Severe Tropical Cyclone Pam, a maximum category five storm, destroyed homes and crops and contaminated water supplies in Vanuatu, increasing the risk of the spread of infectious and water-borne diseases.

An estimated 110,000 people have no access to safe drinking water, while some 75,000 urgently need shelter, according to OCHA.

Laerke said the money would be used to provide life-saving assistance, including food, water, health care and shelter to people in all of the affected areas, covering 22 of Vanuatu's some 80 islands.

In the two hardest-hit provinces, Shefa and Tafea, "all crops... have been damaged or destroyed and food is running out as I speak," Laerke warned.

In other provinces, as much as 90 percent of shelters, he said "have been wiped out, while roads are impassable and debris is still being cleared."

A full $8.2 million of the appeal would go to help bring food assistance to communities were reserves are running dangerously low, he said.

Laerke said donors had already funded eight percent of the requested amount, or $2.3 million, "which is a good start."

The UN's children's fund meanwhile said $4.8 million of the overall UN appeal would go to helping some 82,000 children, or two thirds of the youngsters in the country, in desperate need of humanitarian assistance.

"Children, especially those in the hardest-to reach islands, are in serious danger right now," UNICEF's Pacific Representative Karen Allen said in a statement, pointing to the "significant risk of disease" due to the acute water shortages, limited medical care and poor sanitation.

Schools have officially reopened, but 80 percent of school buildings were damaged in the storm, UNICEF said.

The International Organization for Migration also launched an appeal Tuesday for $1.0 million to help the Vanuatu government return people to their communities as evacuation centres gradually empty.