Only a quarter of the 2.4m affected have received help, the UN says
International donors meeting in Rangoon have pledged nearly $50m (£25m) in aid to victims of Cyclone Nargis, which struck Burma more than three weeks ago.
The sum is a fraction of the $11bn Burma's military government is seeking to fund relief work.
Some donors said the money depended on foreign aid-workers being allowed into the Irrawaddy Delta disaster zone.
The head of the United Nations has said he hopes Burma's leaders will now face up to the scale of the problem.
"I'm cautiously optimistic that this could be a turning point for Myanmar to be more flexible, more practical, and face the reality as it is on the ground," Secretary General Ban Ki-moon told the BBC.
Burma's Prime Minister, Thein Sein, said more help would be welcome but only if it did not have political overtones.
At least 78,000 people have died as a result of the cyclone and more than 50,000 people are still missing.
The UN believes only a quarter of those needing aid - up to 2.4 million people - have received it.
'Full and unfettered'
More than 40 governments attended the one-day conference hosted by the UN and the Association of South-East Asian Nations (Asean).
Britain and other Western donors said the pledged money was contingent on Burma's generals keeping their promise to give foreign aid-workers greater access to the delta.
The UK's International Development Secretary, Douglas Alexander, said the eyes of the world would be on the Burmese to ensure aid workers were given "full and unfettered" access.
"The humanitarian crisis in Burma is grave and urgent," he told the conference.
"I have told the Burmese ministers that I have met: 'You will be judged not by your words but by your actions' and action is what the world will be looking for in the days and weeks ahead."
A top US official, Scot Marciel, also said further US aid depended on Burma giving disaster experts access to disaster areas.
This was "established practice readily accepted by other nations", he added.
American, French and British military ships full of aid are waiting just outside Burma's waters.
Mr Ban said Burma had begun honouring an agreement struck on Friday to allow in foreign aid-workers.
Douglas Alexander calls for action at the UN aid conference
"I expect the relief effort will run for... six months at least, as we feed and care for those who have lost everything," he said.
The Burmese government is concerned that the foreign naval ships off its shores could somehow be used to launch an invasion, diplomats say.
Prime Minister Thein Sein said on Sunday that Burma would accept supplies by sea only if they came in on civilian boats.
In sight of the conference centre in Rangoon is the home of Aung San Suu Kyi, the opposition leader kept under house arrest by the military.
The opposition National League for Democracy has renewed calls for her release.
Her five-year house arrest is due to expire this week, although the military rulers have previously extended the detention period a number of times.