United Nations disaster experts said it would be days before the full extent of the damage was known in a country ruled since 1962 by military regimes.
Bunkered down in Naypyidaw, the junta's top brass will almost certainly have avoided the worst of the storm.
The military authorities declared a disaster in five states and state media carried footage of soldiers clearing trees from roads and Prime Minister Thein Sein, a lieutenant-general, meeting people sheltering in a Buddhist pagoda.
DEATH TOLL COULD CLIMB
The death toll could climb yet further as authorities slowly make contact with outlying towns and villages along the coast, where weather forecasters had predicted a storm surge of up to 12 feet (3.5 m).
They are also likely to uncover victims beneath some of the buildings that collapsed in Yangon under the force of the cyclone, which had been gathering steam for several days in the tropical waters of the Bay of Bengal.
"It was a direct hit on a major city," said Terje Skavdal, regional head of the U.N. Office for the Coordination of Humanitarian Affairs (UNOCHA).
"The government did warn people to stay inside and that might have had an impact, but the material damage is enormous for sure," Skavdal said.
The UN had made an offer of assistance but was yet to receive a response from the country, he added.
An official at Yangon International Airport said all incoming flights had been diverted to the second city of Mandalay, in the middle of the southeast Asian nation, and all departures from Yangon had been cancelled.
Thai Airways in Bangkok said flights would not resume before Monday.
State media said four vessels sank in Yangon harbour, and jetties in ports had come loose.
By 0900 GMT, Nargis had tracked northeast into northern Thailand, where it was dumping large amounts of rain but with dramatically reduced wind speeds.