The World Food Programme agreed to resume relief flights into Burma after suspending them when government authorities impounded 38 tons of aid it had delivered to the disaster-struck country.
After Cyclone Nargis levelled the low-lying Irrawaddy Delta area of the south-east Asian country nearly a week ago, death toll estimates have grown.
While the government has confirmed 23,000 deaths and another 42,000 missing, UN officials on Friday estimated the death toll will climb to 63,000 to 100,000 based on reports from 18 aid organizations working in 55 devastated Burmese townships.
In a sign that the Burmese government was more open to receiving aid, it gave permission to a US military aircraft to make one C-130 cargo plane delivery on Monday, Gordon Johndroe, spokesman for the National Security Council, said.
The International Federation of the Red Cross (IFRC) in Geneva said humanitarian aid had reached around 220,000 people, despite logistical difficulties.
Diplomatic efforts to pressure the military junta to allow in more aid were continuing.
US Secretary of State Condoleezza Rice on Thursday talked with the Chinese and Indian foreign ministers, urging them to "use whatever leverage they have with that top decision-making layer in the Burmese regime to get them to reverse the course that they have been on," and allow in further international assistance, State Department spokesman Sean McCormack said.
The UN said it had received pledges of 77 million dollars out of the total of 187 million dollars that it has asked for to fund international relief efforts.
In New York, UN officials said that Nargis could be the worst cyclone to hit Asia since 1991, when 138,000 were killed in Bangladesh.
"Based on assessment of 18 agencies and their assessment in 55 townships, we estimate currently that the number of severely affected population lies between 1.2 and 1.9 million," said John Holmes, the UN undersecretary general for emergency relief efforts.
An estimated 13 million people of Burma's population of 53 million live in areas hit by the cyclone.
Tim Costello, chief executive of World Vision Australia, told reporters through a video link to London that rescue workers were in a "race against time" and warned of an epidemic of "apocalyptic proportions" that could follow the cyclone.
"We certainly know that once an epidemic starts it's difficult to stop and becomes of apocalyptic proportions. The potential for this epidemic is extremely probable," said Costello.
While the UN reported problems acquiring visas for its relief teams, the Red Cross said seven of its people so far had been granted entry and they expected more to enter the country in the coming days.
US Ambassador to the United Nations Zalmay Khalilzad said the UN should reinforce immediately its relief activities before the death toll climbs higher. He said a US warship is off the Gulf of Thailand with 23 helicopters that could be used to ferry aid to Burma in addition to the initial donation of 5 million dollars.
"We are prepared to do more and we urge the Myanmar government to immediately give access to the UN and the entry to all humanitarian personnel regardless of their nationalities," Khalilzad said.
Japan pledged another 10 million dollars while some other Asian nations like Thailand, Vietnam, Singapore and the Philippines pledged between 200,000 dollars and 1 million dollars.