The UN official co-ordinating aid for tsunami survivors has said concrete commitments worth $717m (£382m) have been secured from donor countries.
The UN wants $1bn in immediate aid for regions like Aceh
Speaking after an international meeting in Geneva, Jan Egeland said he was very encouraged by the swift response.
He said the governments had promised to release the cash to help the disaster victims over the next six months.
But he also warned that donor nations must not neglect other humanitarian crises around the world.
Mr Egeland said it was the first time the UN had collected so much money in such a short space of time after a disaster, calling it an "extraordinary effort".
Japan, the biggest donor, is to contribute $250m (£133m) in cash within the next few days, he said, half the total pledge already made by the Japanese government.
Mr Egeland had earlier urged donor countries to release funds more quickly for the relief effort, saying only one-tenth of aid promised had so far been received.
In other developments in the Indian Ocean region:
- The Indonesian army tells foreign aid workers in Aceh to register to travel outside Banda Aceh and Meulaboh
- Sri Lankan President Chandrika Kumaratunga wants to adopt a Tamil child orphaned by the tsunami as a gesture of goodwill towards the Tamil community, an aide says
- An Acehnese man is rescued by an Arab container ship after two weeks drifting at sea following the tsunami
- International police agency Interpol sets up what is thought to be the biggest disaster victim identification centre in history, in the Thai resort of Phuket.
Tuesday's Geneva meeting came five days after UN Secretary General Kofi Annan chaired a donor conference in Jakarta, Indonesia, where he issued a call for urgent aid.
The amount now promised over the next six months is equivalent to 73% of the $977m (£520m) that Mr Annan requested.
The delegates, representing governments and aid agencies, included US aid chief Andrew Natsios, EU development commissioner Louis Michel and senior ministers from Britain, France and Germany.
Mr Egeland, who chaired the 81-nation meeting, said as it opened that about $300m had been committed to projects on the ground in the tsunami-hit region, out of $3.4bn in formally recorded aid pledges.
"We need very quickly more signed contracts, more cash, more concrete commitments to help keep this massive effort going in the next six months," he said.
But he said that the outbreak of disease and starvation that the UN had feared in the wake of the tsunami disaster, in which more than 150,000 people died, did not seem to be happening.
The UN co-ordinator listed at least a dozen regions where UN agencies are struggling to meet the basic needs of millions of people.
He pointed out that the Democratic Republic of Congo, where 1,000 people die daily of preventable diseases or because of the conflict there, suffered the equivalent of a tsunami every five months.
Each year, Mr Egeland said, the UN launches an appeal for aid work but actual funds always fall well short of pledges.
Phil Bloomer, head of UK-based charity Oxfam, said this was "crunch time" to make sure the pledges were realised.
"This is not the time for empty rhetoric," he said, quoted by AFP news agency. "The eyes of the world are on this meeting and we want guarantees that the aid will not be diverted from other disasters and other suffering people."