Makeshift camps are sprouting up in Port-au-Prince
Bottlenecks and infrastructure damage have been holding up aid efforts in Haiti, where Tuesday's earthquake has left as many as 45,000-50,000 dead.
There is little sign of aid supplies beyond the airport, and correspondents cite increasing anger among survivors.
Many are spending another day without food and shelter in the ruined capital.
The US defence secretary said the Haiti relief effort was the main US priority in the western hemisphere, as an aircraft carrier arrived off the coast.
And the chairman of the Joint Chiefs of Staff, Adm Mike Mullen, said a hospital ship and more helicopters would be sent in the coming days, and 9-10,000 troops would be in or off Haiti by Monday.
On Friday, the UN said a total of about $270m (£165m) in international aid had been pledged so far for the relief effort.
It will launch an emergency appeal for $550m later on Friday, UN spokeswoman Corinne Momal-Vanian said.
AT THE SCENE
Nick Davis, Port-au-Prince
People are doing what they can to survive here in Port-au-Prince. Every morning the first jobs of the day involve getting the very basics.
Loaded with old plastic bottles or anything else that can hold water, they fill up where they can. Some from broken pipes from collapsed buildings, that still have a supply.
The relief effort is under way, the near constant buzz of planes landing with supplies can be heard overhead. On the ground the aid is materialising slowly.
There are still bodies on the streets, but for those who can afford it, those who can be identified, a decent burial. I saw six men carrying a roughly carved casket, singing as they walked toward the cemetery.
But for others, a less dignified burial, as mass graves have started to be used across the city.
On the ground, correspondents say there is little immediate sign of a co-ordinated relief effort.
The UN's World Food Programme (WFP) says that in total two million people will need food aid, but that it has so far managed to feed just 4,000.
Meanwhile the head of the charity Medecins Sans Frontieres (Doctors Without Borders) said thousands of people were waiting for surgical treatment in Haiti's hospitals, AFP news agency reported.
Port-au-Prince's small airport is filled to capacity and US air traffic controllers have taken charge of air traffic control to help manage the influx of planes.
However because of fuel shortages, some aircraft are clogging up the tarmac. Meanwhile the port is too damaged to use and roads are blocked by debris.
The BBC's Andy Gallacher in Port-au-Prince says survivors are dying in huge numbers, and clean water, food and medical supplies are desperately needed.
"We hear on the radio that rescue teams are coming from the outside, but nothing is coming," said one man, Jean-Baptiste Lafontin Wilfried.
They want us to provide them with help, which is, of course, what we want to do
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