Burma's state media say a constitutional referendum will be postponed until May 24 in areas hardest hit by Cyclone Nargis, which has killed more than 15,000 people.
Officials fear the death toll could rise even higher.
Burma's military rulers have said the referendum on Saturday will clear the way for democratic elections in 2010, but the tightly-controlled country's opposition says the new charter will reinforce military control.
The government says the ballot will go ahead in the rest of the country - beyond those 47 townships worst hit - as scheduled on May 10, despite the deadly storm.
Officials say at least 10,000 people were killed in the town of Bogalay alone, which is located in the Irrawaddy River delta where the storm swept ashore three days ago.
Thousands of people are missing, while hundreds of thousands are without shelter. Meanwhile, the prices of food and fuel have risen dramatically and witnesses in Burma say anger is building among residents who are complaining about the military's slow response to the disaster.
The storm has created a severe shortage of food and drinkable water.
The government has declared Burma's main city of Rangoon and five central and southern states (Yangon, Ayeyawaddy, Bago, Mon and Karen) disaster areas.
In the wake of the disaster, Burma has told foreign officials and aid organizations that it will accept their help in recovering from Saturday's devastating cyclone.
The United States and several European countries (Britain, Germany, Norway, Sweden) and Asian countries (India, Japan, Singapore, Thailand) have offered assistance. The European Union has pledged $3 million for disaster relief efforts
International groups have expressed concern that aid might not reach the people most in need in the hardest hit parts of Burma.
Some information for this report was provided by AFP, AP and Reuters.