"It's clear that we're dealing with a very serious situation. The full extent of the impact and needs will require an extensive on-the-ground assessment," said Richard Horsey, a spokesman in Bangkok, Thailand, for the U.N. Office for the Coordination of Humanitarian Affairs.
"What is clear at this point is that there are several hundred thousands of people in dire need of shelter and clean drinking water," Horsey said.
Officials from Myanmar's military government met today with representatives of international aid agencies to discuss providing assistance.
Neighboring Thailand announced that it would fly some aid in Tuesday. The private aid agency World Vision said Myanmar's government had invited it "to provide assistance in the form of zinc sheets, tents, tarpaulins and medicine."
The U.S. has approved $250,000 for Myanmar's relief.
The BBC said that in some areas Buddhist monks, who had spearheaded a bloody protest against the government earlier this year, were cleaning up debris and pulling away fallen trees.
"I don't want to say much, but the monks are doing all the clearing up," said a woman in Yangon, also known as Rangoon. "The USDA [the civilian arm of the military junta] have turned up but they're not really doing anything. They're just standing around."
Jens Orback, who identified himself as a former Swedish government minister, was in Yangon when the cyclone struck and told the BBC, "Even in our hotel we couldn't move because of glass falling. We could see trees which must have been standing 100 years falling down."
He said that in the first 12 hours, people were left to dig themselves out of the wreckage.
"There were no policemen and no military on the streets but people were privately out there with their handsaws chopping the trees," Orback said.
A woman in the village of Hlaing Thar Yar outside Yangon said price gouging had become rampant.
"There are now very few buses going into the city and the ones that are running have put up their prices fivefold. Also, the price of corrugated iron to replace our roofs and even nails has skyrocketed," she said.
In Yangon, a man told BBC that essentials instantly became "so expensive" and that the city's water supply has been cut off, doubling the price of candles.
"I think the main water supply has dried up. Even if we use our own pumps we can't get any water out of the mains," he said.
Some people walked to the city's lakes to wash.
Older citizens said they had never seen Yangon so devastated in their lifetimes.
The military, which has ruled for 46 years and is shunned by the West, waited two days before accepting foreign help.
Myanmar's Foreign Ministry officials said they welcomed international humanitarian assistance and urgently need roofing materials, plastic sheets and temporary tents, medicine, water-purifying tablets, blankets and mosquito nets.
The Associated Press and Reuters contributed to this report.