The international Red Cross estimated today that 45,000 to 50,000 people were killed in Haiti's earthquake.
Red Cross spokesman Jean-Luc Martinage said the estimate was based on reports from its network of volunteers across Port-au-Prince.
Countless people remain trapped following the 7.0 magnitude quake, which struck the capital, Port-au-Prince, on Wednesday, destroying thousands of buildings, including the presidential palace. Millions are in need of emergency assistance.
Tremors from dozens of aftershocks prompted terrified Haitians to sleep in parks and on the streets.
Dazed survivors, screaming for loved ones, wandered past bodies as rescuers combed the rubble for those trapped.
The few hospitals still standing, in the poorest country in the Western Hemisphere, overflowed and patients spilled into temporary first-aid tents.
International Red Cross spokesman Paul Conneally said a third of Haiti's nine million people might need emergency aid.
US president Barack Obama pledged US$100 million ($135 million) in aid and called it "one of the largest relief efforts in our recent history".
In Port-au-Prince, one young man yelled in English: "Too many people are dying. We need international help ... No food, no phone, no water, no nothing."
Survivors too scared to return home sang traditional religious songs and prayed for the dead.
Foreigners slept around the pool of the damaged Hotel Villa Creole, and scores of injured Haitians lay outside on the street.
Asked by a reporter how many people had died, Haitian President Rene Preval replied: "I don't know ... Up to now, I heard 50,000 ... 30,000." He did not say where the estimates came from.
US Secretary of State Hilary Clinton postponed her trip to Papua New Guinea, New Zealand and Australia this week so she can co-ordinate US relief efforts from Washington.
The United Nations said at least 16 members of its 9000-person peacekeeping mission, including 11 Brazilian soldiers, were killed.
Its five-storey headquarters in Port-au-Prince was destroyed.
Former NZ Prime Minister Helen Clark, who heads the UN Development Programme, said all her international staff "appeared to be alive and accounted for".
"The UNDP is still working to ascertain the whereabouts of local staff who had left work for the day and have not been able to be contacted so far."
She said efforts were being hampered because landlines and mobile phones were not working.
"The damage to the capital is immense, the human suffering is huge, and the tragedy has taken tens of thousands of lives.
"Recovery from this disaster will require immense international support and will be lengthy."
Rapper Wyclef Jean, who now lives in the US but was born in Croix-des-Bouquets about 13km northeast of Port-au-Prince, was yesterday going home to help.
The 37-year-old was to play at Rotorua's Raggamuffin reggae concert next Saturday but the company promoting the show, Andrew McManus Presents, did not know last night if he would be appearing.
On his website, Jean wrote: "I cannot stress enough what a human disaster this is, and idle hands will only make this tragedy worse. The over two million people in Port-au-Prince tonight face catastrophe alone. We must act now."
He issued an appeal, with his uncle Raymond Joseph - the Haitian Ambassador to the United States - asking people to donate.
The United States and other nations were yesterday sending aid workers and rescue teams to Haiti.
Kate Conradt, of the Save the Children charity in Washington DC, was last night in the Dominican Republic waiting to fly to Haiti with three colleagues to administer aid.
She said workers were assessing damage on foot or by motorcycle, because rubble blocked the roads.
"Three-storey buildings are now one-storey buildings at most," Ms Conradt said.
"They were still hearing buildings collapsing five hours after the first big quake.
- Agencies and Herald staff