YANGON (AFP) - - More than 22,000 people have been killed and 41,000 left missing after a powerful cyclone hit Myanmar last weekend, state television announced late Tuesday.

Aid workers were racing to deliver food and water to the southern coast which was submerged by floodwaters, leaving scenes of utter devastation and desperate homeless survivors running low on food and clean water.

But with the clock ticking four days after the storm hit, Myanmar's reclusive military rulers insisted foreign aid experts would still have to negotiate with the government to be allowed into the isolated nation.

The government also said it would proceed this weekend with a constitutional referendum as part of its slow-moving "road map" to democracy, except in the areas hardest hit by the disaster.

In its first news conference since Tropical Cyclone Nargis barrelled into the Irrawaddy river delta early Saturday, the government said many people died from a 12-foot (3.5-metre) tidal wave that slammed into the area.

Social Welfare Minister Maung Maung Swe told reporters that most of the town of Bogalay, one of the delta areas that bore the brunt of the storm's force, had simply been washed away.

"Ninety-five percent of the houses in Bogalay were destroyed," he said. "Many people were killed in a 12-foot tidal wave."

Satellite images from US space agency NASA showed virtually the entire coastal plain of the country, once known as Burma and now one of the poorest nations on the planet, under water.

The New Light of Myanmar newspaper, which like all media in this impovershed nation is strictly controlled by the junta, had earlier said that 15,000 people were killed.

But it was not known how precise that toll could be given the scope of the destruction. Phone and electricity are not working in many areas, and roads in some places -- where they even existed -- are wiped out.

Christian relief organisation World Vision, one of the few international agencies allowed to work inside Myanmar, said its teams had flown over the most affected regions and witnessed horrific scenes on the ground below.

"They saw the dead bodies from the helicopters, so it's quite overwhelming," Kyi Minn, an adviser to World Vision's office in Myanmar's main city of Yangon, told AFP in Thailand by telephone.

"The impact of the disaster could be worse than the (2004 Asian) tsunami because it is compounded by the limited availability of resources on top of the transport constraints," he said.

Aid groups were rushing to bring food, clean water, clothing and shelter into the country, whose military rulers have long spurned most of the outside world -- and prevented many aid groups from operating in the isolated nation.

In Geneva, the United Nations said it had a disaster-assessment team in neighbouring Thailand still awaiting entry visas -- while the government underlined that foreign relief experts would not be allowed in automatically.

"For expert teams from overseas to come here, they have to negotiate with the foreign ministry and our senior authorities," Maung Maung Swe said.

Relief officials warned that as time went on, fears were mounting about the risk of disease -- on top of the logistical problems of getting aid to many regions that are both remote and densely populated.

"Getting it out to the affected populations will be a major challenge, given that there is widespread flooding," said Richard Horsey, a spokesman for the UN Office for the Coordination of Humanitarian Affairs in Bangkok.

"The urgent need is for shelter and for water. Without clean drinking water, the risk of disease spreading is the most serious concern."

The UN's food agency meanwhile said that the destruction also threatened rice exports, which it was hoped would ease shortages in Sri Lanka and Bangladesh amid soaring global food prices.

Brigadier General Kyaw Hsan, the secretive regime's information minister, said the country was "greatly thankful" for the offers of help that have been pouring in.

But US First Lady Laura Bush, a longtime critic of the military that has run the country for 46 years, said the government had not done enough to warn citizens that the storm was approaching.

The UN's disaster reduction agency was also critical.

"Looking at the number of deaths, it leads us to think that an early warning system had not been put in place," an agency spokeswoman said. "Obviously many people did not have time to evacuate."