Burma was said last night to be facing a catastrophe of “apocalyptic proportions” as the military regime stepped up its obstruction of international relief efforts after the cyclone.

Epidemics of malaria, cholera and dysentery will kill many more than the first disaster, experts declared, as the isolationist regime impounded UN emergency supplies and turned away aid workers.

Last night the White House announced that it had received permission to fly a military C130 transport aircraft into Burma on Monday.

Later, a UN humanitarian affairs official appealed for $187 million (£97 million) of aid and urged a change of attitude from Burmese authorities.

“We are ready to cooperate fully,” Kyaw Tint Swe, Burma’s UN ambassador said. “Regarding access, we hear you and I will certainly report back.”

The junta had earlier said that it was “not in a position to receive rescue and information teams from foreign countries”. Burma would distribute relief supplies “with its own resources”.

Some 5,000 sq km (2,000 square miles) are flooded and corpses are rotting in the open. “The potential for an epidemic is extremely probable,” Tim Costello, a World Vision executive in Rangoon, said. “Once an epidemic starts it’s very difficult to stop and becomes of apocalyptic proportions.” Neoleen Heyzer, the UN’s leading Asia official, said: “There is a small window of opportunity if we are to avert the spread of diseases that could multiply the already tragic number of casualties.”

Burmese officials impounded 38 tonnes of high-energy biscuits – enough to feed 95,000 people – on two UN aircraft. The UN World Food Programme declared that “unacceptable”, and suspended flights into Rangoon, though it will send in two more today. The previous night the regime refused a relief aircraft from Qatar carrying rescue personnel.

In Thailand a small army of relief workers is awaiting permission to enter Burma. Their frustration was compounded by the Burmese Embassy’s closure until Monday because of a Thai public holiday.

“This is too long to wait for people whose lives are at such a precarious balance,” said Paul Risley, a World Food Programme spokesman, describing the blockage as “unprecedented in modern humanitarian relief efforts”.

Many governments muted their condemnation lest they make things worse – but not all. “The Burmese regime is behaving appallingly,” Kevin Rudd, the Australian Prime Minister, said. Angela Merkel, the German Chancellor, backed French calls for the UN Security Council to explore ways of forcing Burma to back down.

Douglas Alexander, the British International Development Secretary, yesterday used his strongest language so far in describing the crisis. “It is appalling and inexcusable that valuable supplies are piling up outside Burma while people inside the country are dying,” he said. Ban Ki Moon, the UN Secretary-General, urged Burma to admit humanitarian workers “without hindrance”. Indonesia called on its leaders to focus on rescue efforts rather than today’s referendum on a constitution strengthening the junta.

The regime is said to be terrified that an efficient international relief effort would weaken its grip on power. “The military regime is extraordinarily xenophobic. They’re afraid of everything,” Sean Turnell, a Burma expert at Macquarie University in Sydney, said.

“They are more concerned with control and maintaining an omniscience in front of their people than saving lives.”

Donations to the British Disaster Emergency Committee can be made by calling 0870 6060900

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