Families displaced from last Saturday's cyclone take shelter at a monastery in Kyauktan Township in southern Burma on Thursday. (Associated Press)

The secretary general of the United Nations is urging Burma to delay its constitutional referendum and focus its attention on helping citizens cope with the aftermath of a devastating cyclone.

Ban Ki-moon said the country should not proceed with its Saturday voting date. Burmese officials have said they are keeping the date, and will only be delaying the vote in the areas most affected by the storm.

"Due to the scope of the disaster facing [Burma] today, the secretary general believes that it may be prudent to focus instead on mobilizing all available resources and capacity for the emergency response efforts," a statement from Ban's office said.

The cyclone struck Burma, a southeast Asian country also known as Myanmar, on Saturday, flattening an estimated 95 per cent of buildings in villages in the southern Irrawaddy Delta. Burmese officials have said more than 22,000 people were killed, but a U.S. official has pegged the death toll at well above 100,000.

The UN believes at least one million people have been forced to flee their homes.

The UN statement said Ban is "deeply concerned" about the welfare of the Burmese people at a time of "national tragedy."

Burma's referendum to approve a new constitution for the country was swirling in controversy in the weeks before the storm struck. Critics said the vote would be rigged by the ruling military junta and would not be fair or democratic.

Burma has not had a constitution since 1988, when the army brutally suppressed pro-democracy demonstrations and quashed the existing constitution.

Some ethnic minority groups say the proposed constitution will give the central government even greater powers.