Myanmar opened polls for hundreds of thousands of cyclone victims, many hungry, homeless and still waiting for aid, in a much-criticised constitutional referendum Saturday ahead of a key donors' conference.

Voters who have been struggling to stave off starvation and disease since the May 2-3 disaster, which left 133,000 dead or missing, left ramshackle shelters and patched-up homes to cast ballots on the military-backed constitution.

The outcome of the balloting has already been decided, after the government declared an overwhelming victory in the first round of voting on May 10, held in parts of the country spared by the cyclone.

The vote comes on weekend of intense diplomatic activity in one of the world's poorest and most isolated countries, which is still reeling from the storm three weeks ago.

UN Secretary General Ban Ki-moon left Myanmar on Friday, saying that he had finally won permission from junta leader Than Shwe for foreign aid workers to enter the country to oversee the relief effort.

The announcement could end a deadlock over the relief effort, and set a more positive tone when Ban returns Sunday for the donors' meeting hosted by the United Nations and the Association of Southeast Asian Nations.

The United Nations has already launched an appeal for US$187 million to fund a relief effort, but Myanmar has put the total storm damage at US$11.7 billion.

Ban is avoiding being in the country during the vote on the constitution, which the junta says will pave the way for democratic elections in 2010. Critics say it will only entrench military rule.

This weekend the regime is also set to extend the house arrest of celebrated democracy leader Aung San Suu Kyi, whose detention comes up for renewal by Monday.

Until the cyclone, winning her freedom had been a key concern of Western countries, which have imposed sanctions on the regime to press for her release.

But political concerns in Myanmar have now taken a back seat to the urgent humanitarian needs of 2.4 million cyclone victims in desperate need of food, shelter and medicine.

Earlier Ban had called on the regime to delay the voting and to focus its resources on helping storm victims, but on his trip here he did not mention the polls or Aung San Suu Kyi.

The government did postpone balloting in parts of the county hit hardest by the storm, but insisted on going ahead with the second round Saturday, despite the human tragedy in the Irrawaddy Delta, where entire villages were washed away by the storm.

Only 25 percent of the people in need have actually received any help, according to the United Nations, creating the prospect that some storm victims could receive ballot papers before getting any aid.

People whose homes were destroyed have told AFP they were forced out of schools where they had sought shelter, so that the classrooms can be used as polling stations.

And the few evacuees lucky enough to live in emergency shelters say authorities have combed through the camps to register everyone over 18 to vote.

Security forces have blocked most foreigners from the hardest-hit regions of the delta, but AFP reporters who have slipped in say that the people are still hungry and homeless, and that some bodies are still floating in the water.

The junta is "still determined to have their referendum when they haven't cleaned up the bodies yet," said Sunai Phasuk, a researcher with Human Rights Watch in Bangkok.

"They want to show that they are in control of the situation," Sunai said, adding that the regime would take no chances on the outcome of the vote.

"They can manufacture the results as what they want. They can fabricate the numbers," Sunai said.

Aung San Suu Kyi's party has urged voters to reject the constitution, which they say will enshrine military rule.

The vote to approve a new constitution is the first balloting in Myanmar since a general election in 1990, when Aung San Suu Kyi's party won in a landslide but she was placed under house arrest.

The new charter would ban Aung San Suu Kyi from ever holding office, while granting the military broad powers to declare a state of emergency and take direct control of the government.