Jan Egeland, the UN undersecretary-general in charge of emergency relief, on Saturday said the overall donations jumped to $2 billion from $1.2 billion primarily due to a $500 million pledge from Japan - the highest single donation to date.
About 40 governments and the World Bank have made pledges.
"We are at the moment recording pledges of $2 billion for emergency phase and recovery phase," Egeland said.
"It's the biggest outpouring of relief in such a short period of time."
He said the total pledges added up to more than all the aid received by the United Nations in 2004 for such places as Sudan's Darfur region and the Democratic Republic of Congo.
Kofi Annan is expected to visit
Indonesia next week
"International compassion has never been like this," he said.
He also disclosed that the UN Secretary-General Kofi Annan was likely to visit tsunami-ravaged Indonesia next week.
Annan has been invited to the Indonesian capital, Jakarta, on Thursday and UN officials said he will probably accept.
The secretary-general had planned to issue a relief appeal on Thursday but some officials said he may do it from Jakarta. Indonesia took the brunt of Sunday's earthquake and the resultant tidal waves and thousands there have perished.
The United Nations is working with the International Committee of the Red Cross and coordinating thousands of independent relief groups to get food, medicine, generators, and transport to the millions of afflicted people.