Many Haitians are living on the streets, fearing that aftershocks will destroy more buildings [EPA]

Aid agencies and the US army are moving to get help to Haiti where thousands of people are feared to be trapped under rubble after an earthquake which is believed to have left tens of thousands dead.

Aeroplanes from China, France, Spain and the United States landed at Port-au-Prince's airport on Thursday, carrying rescue teams and tons of water, food, medicine and other supplies.

Up to 3,500 troops from the US army's 82nd Airborne Division will be sent to Haiti to help with the relief effort and to provide security in the wake of Tuesday's quake, a US army official said.

The first 100 soldiers from the 82nd Airborne were scheduled to arrive in Haiti on Thursday and would begin preparing for the arrival of other soldiers, Major Brian Fickel told Reuters on Thursday.

The United Nations has mobilised 37 search and rescue teams from a global network to the devastated capital Port-au-Prince.

But more than 48 hours after the 7.0 magnitude quake struck, only very limited help was available to those affected by the quake.

Waiting for rescue

The Haitian Red Cross said it believed that 45,000 to 50,000 people had died in the earthquake.

About 7,000 people killed in the earthquake have already been buried in a mass grave, Rene Preval, Haiti's president, has said.

Barack Obama, the US president, on Thursday announced that the US would provide an aid package to Haiti worth $100m.

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Haitians struggle to cope amid aftermath
of devastating earthquake

"To the people of Haiti, we say clearly and with conviction, you  will not be forsaken, you will not be forgotten," he said.

He said the US would grant "every element of our national capacity, our diplomacy, and development assistance, the power of our military and  most importantly, the compassion of our country" to Haiti.

Numerous bodies are lying amid collapsed buildings in Port-au-Prince, and the cries of people buried beneath rubble have continued to ring out.

The director of Port-au-Prince's general hospital said that at least 1,500 bodies had been stacked inside and outside the building by 11am (1600GMT) on Thursday.

"I can't say how many more bodies will be brought here," Guy LaRoche told Reuters.

Sebastian Walker, Al Jazeera's correspondent in Port-au-Prince, said that the scene in Haiti is "absolutely unimaginable".

"Buildings have collapsed like pancakes, trapping people, cars ... you can see limbs sticking though the rubble. It is a horrific scene. Thousands of people are in the streets and many are carrying suitcases, looking to leave the city and go to the provinces.

"We have seen more aeroplanes [carrying aid] arrive this morning. There is a stark difference from last night - there were no emergency workers during our visit from the airport to [the centre of Port-au-Prince] then.

"It looks like the aid operation is kicking into action now, which is at least some cause for optimism."

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Kathryn Bolles, an emergency help expert with Save the Children in Santo Domingo, the capital of neighbouring Dominican Republic, said that the agency was working as quickly as it could to provide help to those affected by the quake.

"Currently, Save the Children is housing families in the neighbourhoods [surrounding Port-au-Prince] to prevent them from having to hike 10 miles to get up to our facility," she told Al Jazeera on Thursday.

"The situation for children and families in Haiti was dire to begin with and they are still recovering from the 2008-2009 hurricane. Many hospitals, schools, churches damaged then [had] still not been repaired [by the time of the earthquake].

"Right now, the immediate need seems to be food and water. Our team is bringing pallets of water, donated food from supermarkets in the Dominican Republic and boxes of antibiotics and surgical trauma equipment."

Many people were gathered in Port-au-Prince's parks, either sleeping on the ground or under makeshift tents as they waited for aid to arrive.

Ansel Haerz, a journalist in Port-au-Prince, told Al Jazeera that, in the absence of international rescue workers, the people were working together to dig through the debris for survivors.

"Haitians are coming together, I have seen them many times, crowded around a little spot in a building where there is a little space trying to hear if anyone is trapped beneath it and trying to get people out," he said.

'Big priorities'

John Holmes, the UN humanitarian affairs chief, told Al Jazeera that the world body was doing "all that it can to respond to the emergency".

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"One of the big priorities is getting enough doctors, medical teams and hospital staff on the ground, then food, clean water and shelter," he said, adding that the situation was "dire".

He warned, however, that these emergency operations take time.

"At this point in time, we cannot get teams instantly there, or as quickly as we would like, particularly in emergency situations like earthquakes where the hours count," he said.

Peter Jensen, an assistant professor at the University of Copenhagen and leader of a Masters programme in Disaster Management, said that the scale of the quake was likely to hinder the speed of emergency relief efforts.

"Haiti is a very special case because only 15 months ago the international community was there when there were big floods in Gonaives. After those floods, it was fairly obvious that Haiti needed preparation plans, which can now be brought out in the open," he told Al Jazeera on Thursday.

"The problem now, however, is that the normal government structures and the local UN structures have collapsed. Then, we have some serious problems."

Casualty fears

Hillary Clinton, the US secretary of state, compared the disaster to the 2004 Indian Ocean tsunami that killed more than 220,000 people.

Scenes of devastation could be seen throughout the capital Port-au-Prince [AFP]

"The Indian Ocean tsunami was such a terrible tragedy and with such high loss of life. This will be a very high loss of life as well," she said.

Clinton said that she was shortening her Asian tour to return to the US to help tackle the crisis.

The sheer number of dead bodies was expected to pose a problem.

The World Health Organisation said it had sent specialists to help clear the city of corpses, and the International Red Cross was sending a plane loaded mainly with body bags.

Reports from witnesses in Port-au-Prince said that looters had prowled through shops before blending into crowds of refugees lugging salvaged possessions.

Security fears were also heightened after the United Nations said the main prison in the capital had collapsed, allowing some inmates to escape.

Several thousand Haitian police and international peacekeepers poured into the streets on Wednesday to clear debris, direct traffic and try to maintain security.

Peacekeepers killed

A spokesman for the United Nations mission in Haiti said on Thursday that at least 36 UN workers had been killed in the earthquake.

About 150 UN staff remain unaccounted for after its main building in the capital was severely damaged, according to estimates by the world body.

The increased UN death toll was announced a day after Preval said that Hedi Annabi, the chief of the UN mission in Haiti, had been killed.

But Holmes said he could not confirm if Annabi was dead and said that the UN was "trying not to be distracted by our own casualties".

"Our first priority is to help the Haitian people, get them out and save them while they're still alive," he said.

Already one of the poorest nations in the Americas, Haiti has been hit by a series of recent disasters, including deadly hurricanes in 2008.

Tuesday's quake - along with the more than 30 aftershocks measuring up to 5.9 in magnitude - was the latest tragedy to hammer the country, which has been scarred by years of unrest, crime and political tumult.

Source: Al Jazeera and agencies