The Red Cross estimates 50,000 people have died in Haiti's devastating earthquake, as rescue teams race against time to find survivors and residents grow increasingly desperate for aid.
Red Cross believes a further three million people may be injured or homeless in the wake of the 7.0 magnitude quake which hit near the capital Port-au-Prince on Tuesday.
There is a growing sense of desperation as time goes by with little or no relief. The United States is sending up to 3,500 troops and 2,200 marines, but aid is so far only trickling in, though some search and rescue teams are on the ground.
Many Haitians have shown patience so far but the mood is changing, the BBC reports, as survivors wait for urgently needed medical supplies, clean water and food.
Entire schools, communities and police stations have been destroyed and the voices that were being heard in buildings reduced to rubble have fallen silent.
For many people, the promise of help from other countries is too little, too late. Those that survived the massive earthquake are now dying in huge numbers.
Seven thousand bodies have already been buried in mass graves. A witness in Port-au-Prince reports angry residents are blocking roads with bodies in protest at the delay in aid reaching them.
About 1500 corpses are piled up outside the main hospital and bodies litter many streets.
The search for survivors continues, but rescuers lack heavy lifting equipment and many are using their bare hands.
Many residents are spending a third night on Wednesday without shelter or in makeshift camps in the ruined capital. Others are leaving the city in droves.
Aid efforts hampered
A worldwide effort to help victims of the earthquake is being hampered by inadequate or shattered infrastructure in western hemisphere's poorest country.
Planes carrying aid have begun arriving, but there is serious congestion at the Port-au-Prince airport.
The airport is busy but chaotic, with relief planes jostling for space in the small unloading area next to the runway, the BBC reports.
Many have been delayed by the limitations of the airport and some planes have been forced to land in the Dominican Republic, due to bureaucracy and red tape.
Some of the planes are full of medical supplies, others have expert rescue teams from South American countries, Europe and the United States.
It is far from clear how effective the distribution of aid may be. There are problems of coordination with the Haitian government, and some roads are reported to be blocked by buildings toppled in the quake.
United States personnel have taken over air traffic control at the airport serving Port-au-Prince. Earlier, Haiti aviation authorities restricted flights, fearing planes would run out of fuel while waiting to land.
An ABC reporter in Haiti said two C-130 planes almost collided in the confusion as more than a dozen flights were banked up trying to land on Thursday.
US commits $100m in funding
US President Barack Obama has pledged $US100 million for Haiti quake relief and has enlisted two former American presidents to help raise more.
Mr Obama has told his top aides that responding to the tragedy should be their top priority. He has directed his administration to launch a swift, coordinated and aggressive effort to save lives and support recovery in Haiti.
Mr Obama said one of the biggest relief efforts in America's history was moving towards Haiti.
"More American search-and-rescue teams are coming, more food, more water, doctors, nurses, paramedics, more of the people, equipment and capabilities that can make the difference between life and death."
The US is sending up to 3,500 soldiers from an airborne division, along with an aircraft carrier and three amphibious ships with 2,200 marines to support the rescue effort.
Former presidents Bill Clinton and George W Bush have agreed to Mr Obama's request to lead private sector fundraising efforts.
Internet giant Google is donating $US1 million and internet resources to aid organisations on the ground in Haiti.
Meanwhile, rescue crews with specialist equipment and medical and food supplies are also arriving by air from several other countries including China, Britain, Canada and France.
United Nations World Food Programme spokesperson Bettina Luescher said the organisation is mobilising people from all over the world to bring in what is needed.
"Its a huge task, the people of Haiti need everything and they need it now," she told the BBC.
"Just in a normal day, the World Food Programme would be feeding one million or two million people a day in Haiti, and now we need to do even more".