About 20,000 homes have been destroyed and 90,000 people made homeless on the island alone, a government official said.
The death toll is expected to rise further, as the situation in remote areas becomes clear.
Military and police personnel have been carrying out rescue operations.
In Irrawaddy's Labutta township, 75% of buildings collapsed and 20% had their roofs ripped off, state TV said.
Cyclone Nargis has since moved towards Thailand where storm warnings have been issued. However, it appears to be lessening in force.
In Rangoon, internet and phone connections have been down since the storm drew near, making it difficult to confirm the extent of the damage.
Official media report that four people were killed and four vessels sank in the former Burmese capital's harbour.
Footage of the damage caused by the cyclone
One Rangoon resident described the damage in the city for the BBC Burmese service: "Everything was wrecked. Roofs of the houses and satellite dishes were blown away."
A Rangoon-based diplomat quoted by Reuters news agency described the city as an "utter war zone".
RECENT TROPICAL STORMS
Cyclone Sidr, 2007, Bangladesh - about 3,500 dead
Typhoon Durian, 2006, Philippines, - at least 450 dead
Typhoon Xangsane, 2006, Philippines - 279 dead
Typhoon Saomai, 2006, China - about 460 dead
Typhoon Bilis, 2006, Philippines, China - 672 dead
Hurricane Katrina, US, 2005 - at least 1,800 dead
Anthony Craig, a regional official of the UN World Food Programme based in Thailand, said that judging from the damage caused to solid buildings in Rangoon, damage elsewhere was likely to be extensive.
"We're seeing a lot of trees down, a lot of billboards blown away, roofs of houses gone, so that is worrying when you consider the type of construction that is there, compared to the type of construction that is elsewhere," Mr Craig told the BBC.
A trishaw driver in Rangoon, who did not want to be identified, complained that the security forces were not doing enough to help.
"Where are all those uniformed people who are always ready to beat civilians?" he asked.
"They should come out in full force and help clean up the areas and restore electricity."
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