State television showed pictures of Ten Sin, the prime minister, convening an emergency meeting of the military government.
There were reports of extensive damage around the country.
Witnesses in Yangon said that hundreds of houses had their roofs blown off and the storm cut electricity as well as phone services in much of the city.
Residents ventured out on Sunday to buy construction materials to repair their homes.
|The Irrawaddy Delta has been the province|
worst hit by Cyclone Nargis [Al Jazeera]
The worst hit area was the Irrawaddy Delta.
Villagers said half the buildings in many towns were damaged or destroyed.
Tens of thousands of people were made homeless in the Irrawaddy Delta last August after unusually heavy rains triggered floods in the low-lying region.
Some people interviewed said that the government had done little so far to help with the clean-up.
a UN official in Yangon, who requested anonymity, told the Associated Press news agency: "It's a bad situation. Almost all the houses are smashed. People are in a terrible situation.
"All the roads are blocked. There is no water. There is no electricity."
Speaking on the situation in Myanmar from Bangkok, the Thai capital, Tony Craig, of the World Food Programme, told Al Jazeera: "The situation now is very uncertain [regarding] the exact extent of the calamity, but obviously this is a severe event.
"If you are in a state where the food situation or malnutrition is a problem and you [receive] a shock to your security, obviously that will be a problem.
"We are prepared to act in these situations - we have put our global response capability on standby."
The storm was initially forecast to move northeast towards Thailand, which warned that flash floods could hit the north, centre and east of the country.
An official at Yangon International Airport said on Saturday that all incoming flights had been diverted to the second city of Mandalay, and all departures from Yangon had been cancelled.
An official at Thai Airways in Bangkok said the airline planned to resume flights on Sunday.
The cyclone comes at a delicate time for Myanmar, which is scheduled to hold a referendum on May 10 on the country's military-backed draft constitution.
A military-managed national convention was held intermittently for 14 years to lay down guidelines for the country's new constitution.
The ruling generals' handpicked delegates included those representing workers.
The new constitution is supposed to be followed in 2010 by a general election.
Both votes are elements of a "roadmap to democracy" drawn up by the generals, who have been in power for two decades.