Up to 1 million people may be homeless after Cyclone Nargis, some villages have been almost totally eradicated and vast rice-growing areas are wiped out, the World Food Program said.

Some aid agencies reported their assessment teams had reached some areas of the largely isolated region but said getting in supplies and large numbers of aid workers would be difficult.

Images from state television showed large trees and electricity poles sprawled across roads and roofless houses ringed by large sheets of water in the Irrawaddy River delta region, which is regarded as Myanmar's rice bowl.

"From the reports we are getting, entire villages have been flattened and the final death toll may be huge," Mac Pieczowski, who heads the International Organization for Migration office in Yangon, said in a statement.

Shari Villarosa, the top American diplomat in Yangon, told NBC's "Today" show that the cyclone had knocked huge trees in the country's largest city.

"And it blew down a significant portion of them, some of these are 6, 8, 10 stories tall — huge trees, 6 feet, 5 feet in diameter. So they came down on roofs," she said.

State radio also said that Saturday's vote on a military-backed draft constitution would be delayed until May 24 in 40 of 45 townships in the Yangon area and seven in the Irrawaddy delta, which took the brunt of the weekend storm. It indicated that the balloting would proceed in other areas as scheduled.

The decision drew swift criticism from dissidents and human rights groups who question the credibility of the vote and urged the junta to focus on disaster victims.

Myanmar's generals have hailed the referendum as an important step forward in their "roadmap to democracy." It offers the first chance for voters to cast ballots since 1990, and the probability is high they will approve the constitution — a legal framework the country has lacked for two decades.

But critics, including the United Nations, the United States and human rights groups, question whether it will lead to democracy.

Myanmar has been under military rule since 1962. Its government has been widely criticized for suppression of pro-democracy parties such as the one led by Nobel Peace Prize laureate Aung San Suu Kyi, who has been under house arrest for almost 12 of the past 18 years.

At least 31 people were killed and thousands more were detained when the military cracked down on peaceful protests in September led by Buddhist monks and democracy advocates.