Myanmar's junta on Saturday pushed ahead with a vote on a new constitution, ignoring calls from the United Nations to focus on delivering aid to 1.5 million cyclone victims facing disease and hunger.

The referendum being held in all but the most devastated parts of the country is the first balloting to take place in Myanmar in nearly two decades.

Voting was postponed by two weeks in the main city and former capital of Yangon, as well as most of the Irrawaddy delta where Cyclone Nargis struck last week, leaving 65 000 dead or missing according to the junta's count.

Despite growing fears for survivors left without food or shelter, the regime has refused to allow in foreign aid workers to direct the relief effort, drawing condemnation from the UN and world leaders who urged the ruling generals to open their doors.

Although Myanmar says it will now accept aid from the United States, it has tussled with the World Food Programme over unloading UN supplies, triggering a brief suspension of the global body's relief flights on Friday.

The UN has launched an emergency appeal for $187-million to help the cyclone victims, but Secretary General Ban Ki-moon has not yet succeeded in speaking directly with the reclusive junta leader Than Shwe, a UN source said.

Than Shwe (75) ignored calls to delay the referendum and allow in foreign experts, despite warnings that without international aid, people who survived the storm's onslaught in the delta could face a new tragedy as disease and hunger stalk the region.

Detained democracy leader Aung San Suu Kyi's party has slammed the junta for proceeding with the vote in the wake of the cyclone, with some polling stations in the delta set up just blocks from makeshift shelters crowded with evacuees whose homes were destroyed.

The regime says the charter will clear the way for democratic elections in two years, but critics say the document will ensure the generals remain dominant in a country that has been ruled by the military for nearly half a century.

Aung San Suu Kyi's party, which won elections in 1990 in a landslide but was never allowed to govern, has called on voters to reject the constitution, but has had little means of spreading its message.

Her National League for Democracy is not allowed to have any offices outside the main city and former capital, which was itself devastated by the storm.

Speaking publicly or passing leaflets about the referendum is illegal, and the opposition has no access to the tightly controlled national media, which has been broadcasting propaganda tunes promoting the charter.

"With this situation, it is not the appropriate time to hold the referendum," NLD spokesperson Nyan Win said.

The situation on the ground is one of horror — with starving survivors picking for food in waterways littered with the bodies of the dead — and aid groups agree time is running out.

Countless masses are suffering in the waterlogged southern delta, where entire villages were washed or blown away.

"I am angry with the government," said Dowla Shwe, a single mother with five children who said her house was one of the many that simply vanished when the powerful storm tore through her village.

She said the military had brought no aid or food — and that she feared her children would now starve to death.

"If they can't help," she said, "why not allow foreigners to come and help us?"

Aid groups have repeatedly said that foreign experts who specialise in moving aid through disaster zones and assessing which regions need help first are essential to keep more lives from being lost in the tragedy.

"The situation is getting critical," said Noeleen Heyzer, the top UN official for Asia.

"There is only a small window of opportunity if we are to avert the spread of diseases that could multiply the already tragic number of casualties."

Critics of the regime have also warned relief organisations that if they do not supervise the aid supplies handed over, they may be snatched by the generals and never reach the victims in Myanmar, one of the world's poorest nations.

AFP