The UN has sharply increased its estimate of those severely affected by Burma's cyclone to 2.5m people.
The figure was revised up from the 1.5m previously thought to be in need, following the storm 12 days ago.
Since Cyclone Nargis struck, hardly any foreign aid workers have been allowed into Burma to hand out relief supplies.
Latest Burmese official figures put the death toll at almost 38,500 with 27,838 more missing but the Red Cross warned as many as 128,000 could be dead.
UN Secretary-General Ban Ki-moon said he "regretted" the UN had spent more time arranging rather than delivering help, amid claims of stonewalling by the junta.
Undercover reporter says aid is still in short supply in Burma
Under pressure from Britain to call an emergency summit, Mr Ban convened talks with donors and the Association of South-East Asian Nations in New York on Wednesday.
"Even though the [Burmese] government has shown some sense of flexibility, at this time it's far, far too short," he said.
Thai leader Samak Sundaravej flew to Rangoon for talks with Burmese Prime Minister Thein Sein, but said the junta was adamant it needed no outside help.
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EXTENT OF THE DEVASTATION
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"He insisted that his country [could] tackle the problem by themselves," Mr Samak said in Bangkok after his day trip to Burma.
Fresh storm fears eased on Wednesday as forecasters said a tropical depression off Burma's coast had weakened and was unlikely to brew into a cyclone.
The Joint Typhoon Warning Center in Hawaii downgraded the cyclone risk to "poor".
Meanwhile, the UN accused the generals of beefing up security on checkpoints to keep out foreigners.
John Holmes, the UN's head of humanitarian assistance, says although over 100 international UN aid workers were now in Burma, they were not being allowed into the worst affected area, the Irrawaddy Delta, to distribute aid.
The UN's food agency fears Burma will face food shortages |
EU envoy Louis Michel is heading for Burma for a three-day visit, but he said his chances of making any headway with the junta were "slight".
Residents have told the BBC's Burmese service how private citizens have been trying to distribute water and supplies from their own cars - but soldiers have been confiscating the goods.
A BBC correspondent said one devastated village - with one in four of its 400 homes left standing - had received just one bag of rice from the government.
