Prime Minister Kevin Rudd has made an impassioned appeal to Burma's military rulers to allow international aid agencies access to their country following one of Asia's worst natural disasters.

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Five days after the disaster, which killed more than 22,000 and left nearly twice as many missing, there were few signs of police or soldiers to assist the estimated hundreds of thousands of homeless in Rangoon, Burma's main city.

Video: World calls on Burma to let aid in

Interview: Journalist Matt Davis in Rangoon

Interview: ANU Burma expert Monique Skidmore

Residents said they were mostly left to clear debris on their own or with help from monks, sparking criticism from aid groups that the ruling generals, who have long spurned the outside world, had not issued visas to enter.

Mr Rudd said the immediate problem was to ensure proper access for aid groups and proper coordination for rescue efforts.

"Forget politics, forget the military dictatorship, let's just get aid and assistance through to people who are suffering and dying as we speak, through a lack of support on the ground," Mr Rudd told reporters in Perth.

"That's a direct appeal to the government in Burma."

The United Nations, the United States and other governments also ramped up pressure on Burma's junta to give open access to aid organisations desperate to help survivors.

"We are trying to get maximum cooperation from the government," Rashid Khalikov, a top emergency relief official from the United Nations, told reporters in New York.

"We applied for visas. We have not got the visas. This is a critical moment for the affected populations."

In Washington, US President George W Bush said: "Our message is to the military rulers: 'Let the United States come to help you, help the people'."

"We want to do a lot more. But in order to do so, the military junta must allow our disaster assessment teams into the country."

Australia stressed it was "ready, willing and able" to help, and today announced an initial $A3 million in immediate aid.

Foreign Minister Stephen Smith urged Burma's junta to "allow the independent agencies in to do the usual examinations to work out the most effective way of supplying that aid".

The junta yesterday said foreign experts wanting to come in would need to "negotiate" with the government, which has long been distrustful of any foreign presence here and keeps strict controls on outside organisations.

But delays in the relief effort could have dire consequences, health experts say.

There are fears of mass outbreaks of disease, both in Rangoon and the even harder-hit remote south, as untold numbers of people had no fresh water to drink or bathe in, and many were left to sleep out in the open.

Aid workers who yesterday flew over parts of the south, where entire villages were washed away, reported scenes of utter devastation - rice fields strewn with bodies, and not enough food, water or shelter for survivors.

'Millions' left homeless

A senior official from aid agency Save the Children said millions of people in Burma have been left homeless.

"There are millions of homeless, but how many millions we don't know," he said by telephone from Burma's main city, Rangoon.

Witnesses have reported seeing few soldiers or police joining the relief effort after the weekend cyclone.

Some foreign aid, particularly from fellow nations in Southeast Asia, has been trickling into the country - one of the poorest nations on the planet.

Thailand airlifted in 30 tonnes of medical supplies today - the second delivery to its neighbour in two days. Thailand's public health ministry said it had 40 medical teams on stand-by who had not been given visas to come in.

In the past the junta has proved its willingness to ignore international opinion, and it was not immediately clear what effect the criticism about the visas would have.

It declined international assistance following the 2004 Asian tsunami, and has repeatedly rejected complaints about its long detention of democracy icon Aung San Suu Kyi and its slow-moving efforts to restore democracy.

Yesterday it said that a constitutional referendum set for this coming weekend would still go ahead in most parts of the country despite the tragedy, a move Aung San Suu Kyi's party called unacceptable.

A state newspaper today reported that the government had sent back a BBC reporter who had tried to enter with a tourist, not journalist, visa.