The government’s response to the crisis has drawn international criticism that echoes the condemnation it received after its brutal suppression of demonstrations for change last September. Its usual wariness toward outsiders is widely believed to have been heightened by a national constitutional referendum scheduled for Saturday that would enhance the power of the military junta.

Myanmar’s leaders said they would postpone the vote in only the hardest-hit parts of the country. Secretary General Ban Ki-moon of the United Nations urged the junta’s senior general, Than Shwe, on Thursday to delay the referendum altogether and to allow aid workers into the country to do their jobs.

There are thousands of aid workers inside Myanmar already. Save the Children has a staff of 500 there and has been able to provide 63,000 families with plastic sheeting, food, water purification tablets and other supplies. CARE has a staff of 500, Doctors Without Borders has staff members there, and the United Nations has 1,500 people in Myanmar.

But the scale of the disaster dwarfs these measures, aid experts say. Without a huge influx of supplies and transportation in the area, where many villages were accessible only by boat or helicopter to begin with, the workers can offer only limited help, aid officials said.

“It’s highly frustrating for everyone,” said Ms. Fore, whose agency has relief teams, helicopters and ships offshore, all waiting for visas. The French and British Navies find themselves similarly blockaded. American State Department officials spoke Thursday of air-dropping supplies, but said they would not do so without the junta’s permission.

Many people in the worst-hit areas have not had any food or safe drinking water or medical treatment since the cyclone hit, said the spokesman for the United Nations’ World Food Program, Paul Risley. The storm has mixed drinking water and sewage, posing a severe risk of diarrheal diseases, and flooding has left vast pools of standing water where mosquitoes can breed and spread malaria and dengue fever.

The cyclone struck a country particularly ill equipped to deal with a public health catastrophe, said Dr. Chris Beyrer, an epidemiologist at Johns Hopkins who has worked extensively in Myanmar. Under the military government, the public health infrastructure has been crumbling for decades, he said.