Haiti earthquake death toll 'may be
50,000'
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.
The Red Cross estimates that up to three million people in Haiti have been affected by Tuesday's earthquake.
President Obama: 'Search and rescue teams are actively working to save lives'
Many are preparing to spend another night without shelter or in makeshift 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
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.
However he warned it would take time for much-needed help to reach people.
Mr Obama also promised an immediate $100m for Haiti's relief effort and said that investment would grow over the coming year to aid long-term recovery.
The first 100-strong contingent from the US Army's 82nd Airborne Division was expected to arrive in Haiti by the end of Thursday, with several hundred more due by Friday.
The USS Carl Vinson aircraft carrier and the USS Bataan, carrying a marine expeditionary unit, are on their way.
Gen Douglas Fraser, head of the US Southern Command, told reporters that logistics would be the key to providing relief and that US forces would strive to make Port-au-Prince's port functional again.
The US Federal Aviation Authority earlier temporarily stopped civilian relief flights to Haiti at the Haitian government's request because there was not enough space on the ground for more planes. They have since resumed.