On the ground in Haiti with survivors as they desperately plead for help
The Red Cross estimates 45,000-50,000 people have died in Haiti's devastating earthquake, as rescue teams race against time to find survivors.
The US is sending up to 3,500 troops and 2,200 marines but correspondents say aid is so far only trickling in.
President Barack Obama pledged one of the biggest relief efforts in recent US history and said Haiti would "not be forgotten" in its hour of need.
Aid groups say they need food, water, medical supplies and lifting equipment.
President Obama and French President Nicolas Sarkozy, working with Brazil, Canada and other countries, will organise a conference on reconstruction in Haiti, the French presidency has announced.
The Red Cross estimates that up to three million people in Haiti have been affected by Tuesday's earthquake.
Haitian president speaks of sadness
Many are spending another night without shelter or in makeshift camps in the ruined capital, Port-au-Prince.
Correspondents there say bodies are piling up in the streets and there is still no sign of a co-ordinated relief effort.
Speaking in Washington on Thursday, Mr Obama said some US rescuers were already on the ground in Haiti and more were on their way.
He promised the country "every element of our national capacity, our diplomacy, and development assistance, the power of our military and most importantly, the compassion of our country" following the disaster.
"To the people of Haiti, we say clearly and with conviction, you will not be forsaken, you will not be forgotten," he said.
AT THE SCENE
Andy Gallacher, BBC News, Haiti
Haiti is at a critical juncture at the moment.
I've come across two schools that have completely collapsed, you could see the bodies trapped inside - but there were no rescue teams on the ground. I haven't seen anyone in the two days I've been here.
Haitians are still digging through the rubble with their hands. The bodies are beginning to build up, both on the streets and in public spaces.
There are no coffins here, no arrangements for burials. There is no sense that the promised relief efforts have begun in earnest.
UN emergency relief co-ordinator John Holmes said search and rescue teams were the first priority and had begun to arrive in Haiti.
"They're now beginning, I hope, to make a difference. Every hour counts for this, as you know," he said.
"And of course we're trying to get the medical aid in as fast as possible but it's clear that the local facilities are overwhelmed. We need to get more doctors, field hospitals and supplies on the ground."
The BBC's Matthew Price in Port-au-Prince says Haiti is in massive need of food, water and medicine, as well as bulldozers and heavy lifting equipment.
But perhaps more than anything it needs someone to take charge here, our correspondent says. The government is fragile at the best of times and there is no sense it is able to do anything for now.
The director of Port-au-Prince's general hospital said that by 1100 (1600 GMT) at least 1,500 bodies were already stacked inside and outside the mortuary, with police continuing to bring more corpses on pick-up trucks, Reuters reports.
Ban Ki-moon: "Haiti will need every ounce of help we can offer"
A United Nations spokesman in Haiti, David Wimhurst, said 188 UN staff remained unaccounted for following the collapse of the organisation's HQ in Port-au-Prince and that 36 UN military and police personnel were confirmed dead.
UN Secretary General Ban Ki-moon said it could be days before even an estimate of the overall death toll from the earthquake could be made, but said he feared it would be "very high".
On a note of hope, he recounted the survival of an Estonian UN official who was detected under 4m (13ft) of rubble after scratching noises were heard. He was dug out and is now in hospital.
Mr Ban also praised the readiness of the international community to help.
A British rescue team with heavy lifting gear and dogs has reached Haiti. Other plane-loads of rescuers and relief supplies are being sent from China, the EU, Canada, Russia and Latin American nations.
Cuba had more than 300 doctors in Haiti before the earthquake and they have been treating the injured in field hospitals.
US Secretary of State Hillary Clinton, who cancelled a trip to Asia to deal with the crisis, said Haiti's recovery was "going to be a long-term effort".
The World Bank is funding $100m of emergency aid.
The World Food Programme is working on supplying 15,000 tonnes of food and the Red Cross has begun a $10m appeal.
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