A man stands in Rangoon Wednesday at a pier destroyed by Cyclone Nargis on Saturday. (Associated Press)

More than 100,000 people may have perished in the deadly cyclone that ravaged Burma, a U.S diplomat said Wednesday, adding that the situation is becoming "increasingly horrendous."

"The information that we're receiving indicates that there may well be over 100,000 deaths in the delta area," Shari Villarosa, who heads the U.S. Embassy in the capital Rangoon, told reporters.

She said 95 per cent of the buildings were destroyed in the Irrawaddy Delta, and that food and water are in short supply. Crowds of hungry people stormed the few shops that have opened in the region, sparking fist fights, said United Nations World Food Program spokesman Paul Risley.

So far, the official death toll released by the Burmese government is 22,500, with more than 41,000 people missing.

"There is a very real risk of disease outbreaks as long as this continues."

Waiting for visas

The new estimates come as UN officials warn that delays in issuing visas to relief workers are hampering aid efforts and increasing the risk of a major health crisis.

A number of agencies continue to wait to be granted entry visas by the military junta, which has ruled the country since 1962. Aid groups and governments are asking Burma's military rulers, wary of international scrutiny, to relax their tight grip on the country to allow humanitarian help into flood-ravaged areas.

Burma's government authorized the United Nations to send in emergency supplies from Italy on Wednesday. It remained unclear where the UN aircraft, carrying 25 tonnes of aid, would land in Burma, also known as Myanmar, said Elisabeth Byrs, Geneva spokeswoman for UN relief efforts.

But permission was still pending for a UN co-ordination team to accompany the flight, Byrs said.

U.S. Secretary of State Condoleezza Rice on Wednesday urged the junta to allow international aid into the country as American officials said planes and aid workers are in a position to help.

"What remains is for the Burmese government to allow the international community to help its people. It should be a simple matter. It is not a matter of politics," Rice told reporters in Washington.

A U.S. air force C-130 has landed in neighbouring Thailand and another was on the way, air force spokeswoman Megan Orton said Wednesday at the Pentagon. A rapid deployment unit designed to be the first people inserted into an operation already works out of Thailand and is on hand as well, she said.

Time is of the essence

Burma has put a minister in charge of providing visas for aid agencies, as supplies continue to trickle in for as many as one million people left homeless by the storm.

Relief workers have warned that time is of the essence for bringing in vital supplies — including food and water-purification tablets — if a worse humanitarian crisis and higher death toll are to be avoided.

People pass a house destroyed by Cyclone Nargis in Labutta town, 168 kilometres southwest of Rangoon. (Associated Press)

Richard Horsey, Bangkok-based spokesman for the UN Office for the Co-ordination of Humanitarian Aid, told CBC News that it's taking authorities time to fully contemplate the scale of response that is needed, and that international officials with experience can be a vital resource.

"If we don’t get enough aid to the people who need it, there is a significant risk of a second wave to this disaster in the form of water-borne diseases, and they could take a terrible toll."

Relief teams and aid material are waiting to be brought in from Thailand, Singapore, Italy, France, Sweden, Britain, South Korea, Australia, Israel, U.S., Poland, Japan, according to minutes from a UN relief meeting in Geneva that were obtained by the Associated Press.

Burma has accepted aid from traditional friends China, India and Indonesia.

More than 700 tonnes of food have arrived in Rangoon, Burma's largest city.

"Most urgent need is food and water," said Save the Children head Andrew Kirkwood in Rangoon. "Many people are getting sick. The whole place is under salt water, and there is nothing to drink. They can't use tablets to purify salt water."

Save the Children distributed food, plastic sheeting, cooking utensils and chlorine tablets to 230,000 people in the Rangoon area.

Trucks were sent to the delta on Wednesday, carrying rice, salt, sugar and tarpaulins.

Delta remains submerged

Access to the worst-hit areas, however, remains a major problem for aid workers, who can only reach many of the flooded areas by boat or helicopter, which are in short supply. Much of the Irrawaddy Delta remains submerged.

"Basically the entire lower delta region is under water," Horsey said.

He added that the death toll could rise dramatically and that teams "are talking about bodies floating around in the water.

"It's a huge, huge problem just to get these goods out. [This is] a major, major disaster we're dealing with."

Riots reportedly broke out at shops that opened on the delta on Wednesday.

Paul Risley, a spokesman for the UN World Food Program in Bangkok, said his workers reported that people quickly stormed the handful of shops that opened five days after being hit by the cyclone.

"Fist fights are breaking out," he told the Associated Press.

Britain has offered about $9.8 million to help the crisis, and the U.S. offered more than $3 million in aid, while Canada has pledged $2 million.

Global Medic, a Toronto-based organization specializing in water purification systems, is on its way to the region for a two-week mission. The goal is to bring 21 water-purification units and five million water purification tablets to the area, with one tablet able to purify one litre of water.

But the organization is going without having secured the necessary entry visas.

"We didn't want to wait in Canada twiddling our thumbs," Wesley Normington a spokesman for the group, told CBC News. "So basically we're on our way there and we'll find our way in."

With files from the Associated Press