YANGON, Myanmar (CNN) -- The death toll from the Myanmar cyclone is more than 15,000 people, Myanmar's government has said, with at least 10,000 killed in the township of Bogalay alone, according to the Chinese state-run news agency Xinhua.
Survivors were facing their third night without electricity in the aftermath of the historic cyclone that also clogged roads with thousands of downed trees.
Diplomats were summoned to a government briefing Monday as the reclusive southeast Asian country's ruling military junta issued a rare appeal for international assistance in the face of an escalating humanitarian crisis.
A state of emergency was declared across much of the country following the 10-hour storm that left swathes of destruction in its wake.
The death toll of more than 15,000, official sources told Xinhua, makes the weekend cyclone the deadliest natural disaster to hit Myanmar in recent history, according to figures compiled by a U.N.-funded disaster database.
The toll eclipses that from a 1926 wind storm that killed about 2,700 people in the country, according to the database.
The assessment is bleak, Kyi Minn of the international aid group World Vision told CNN Tuesday.
"It could be worse than (the) tsunami," Minn said, comparing the cyclone's impact on Myanmar to the damage caused there following the tsunami that struck the region in late 20
That tsunami was triggered by a a massive earthquake off the coast of Indonesia. It killed more than 150,000 across the region.
Minn said clean drinking water, food, medicine and shelter are all at a premium in southern Myanmar.
The government of neighboring Thailand said Myanmar's leaders had already requested food, medical supplies and construction equipment, AP reported. The first plane-load of supplies was due to arrive Tuesday, a Thai spokesman said.
United Nations Secretary-General Ban Ki-moon said in a statement he was "deeply saddened by the loss of life and the destruction suffered by the people of Myanmar" and pledged to mobilize international aid and assistance as needed.
A United Nations Disaster Assessment and Coordination team is on stand-by to assist the government in responding to humanitarian needs if required, the statement said.
Scenes of the destruction showed extensive flooding, boats on their sides in Yangon harbor, roofs ripped off buildings, uprooted trees and downed power lines after cyclone Nargis battered the Irrawaddy delta with 150 mile (240 km/h) an hour winds throughout Friday night and Saturday morning, dumping 20 inches of rain. 
Watch how the cyclone crippled Yangon »
Residents of Yangon trudged through knee-deep swirling brown waters Monday as the delta city remained mostly without electricity and phone connections.
The U.S. Embassy in Myanmar has issued a "disaster declaration" in the country and authorized the release of $250,000 for cyclone relief efforts, Deputy State Department spokesman Tom Casey said Monday.
A disaster relief team is standing by, Casey said, but the Myanmar government had not given permission for the team to enter the country.
U.S. first lady Laura Bush blasted the military government, saying the lack of warning before the deadly cyclone hit was the latest example of "the junta's failure to meet its people's basic needs."
Hakan Tongkul, with the United Nation's World Food Programme, said residents in Yangon needed urgent assistance. "This has pushed people to the edge. All that they have has been blown away." Watch the cyclone hammer Yangon »
Michael Annear, regional disaster manger for the Red Cross, said the group was helping provide safe drinking water.
Relief agencies met at the United Nations' Bangkok headquarters Monday to coordinate their response to the disaster. The International Federation of Red Cross and Red Crescent Societies said it had released 200,000 Swiss Francs (about $190,000) to help with the aftermath.
A state of emergency was declared Sunday across five regions: the city of Yangon, Irrawaddy, Pegu and the states of Karen and Mon. All flights to Yangon, the former capital, were canceled.
"Most Burmese with whom we've been in touch report they lost their roofs, although so far everyone we have been able to contact reports that they and their families are safe," said a Yangon-based diplomat who requested anonymity because he was not authorized to speak to the media. 
See photos of the destruction »
Most telephone and cell phone service was down in Yangon, a city of about 6.5 million people, according to Dan Rivers, a CNN correspondent in the country.
In some places, the price of fuel had quadrupled to $10 a gallon. Even with that price lines for gas stretched around the block and some sought to buy gas on the black market.
The main water supply has been cut in many areas and power lines are down, Rivers reported.
Earlier Monday, an editor for an independent Myanmar newspaper based in Thailand told CNN that people in the Southeast Asian nation were angry over the response to the disaster by the ruling military junta.
"People are very angry with the slow response coming from the military government," said Aung Zaw of Irrawaddy news magazine. Listen to Irrawaddy journalist discuss the situation in Myanmar »
Khin Maung Win, a spokesman for the Democratic Voice of Burma -- a broadcast media group run by opposition expatriates -- said the whole of the delta region had been affected and entire villages had disappeared.
Pictures from inside the country showed a cyclone-ravaged region with tin huts crushed under trees. Bicyclists navigated around large branches that littered the deserted roads.
A man with his pant legs rolled up waded through knee-deep water and strained to clear massive limbs that were blocking the entrance to a house.
Despite widespread damage, Myanmar's junta plans to proceed with a referendum on the country's constitution on May 10 -- the fourth step of a "seven-step road map to democracy" -- according to state-run media reports. 
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A critic of Myanmar's government said the referendum must be postponed. "They would be very stupid to go ahead with it," said Khin Maung Win with Democratic Voice of Burma, a broadcast media group run by opposition expatriates. "Thousands of people are dying or missing. It is very difficult to get around or get food and water. How can people vote?"
Myanmar, formerly called Burma, last held multi-party elections in 1990, when Aung San Suu Kyi's National League for Democracy handily won. The military junta ignored the results. Suu Kyi, who is currently under house arrest, has been in detention without trial for more than 12 of the past 18 years
