Security fears stalk Haiti as quake survivors await aid
Rescuers pull a child from the rubble of the Haiti earthquake
There are mounting security concerns in Haiti's earthquake-hit capital as distribution problems continue to hamper getting aid to survivors.
Days after the quake devastated Port-au-Prince, killing tens of thousands, there are some reports of gangs preying on residents and looting.
Officials say thousands of prisoners are unaccounted for after the main prison was destroyed.
Relief has been arriving, but little has moved beyond the jammed airport.
Damage to the seaport, roads and other infrastructure has prevented the speedy distribution of food, water and medical supplies.
AT THE SCENE
Matt Frei, BBC News, Port-au-Prince
There are quite a few diggers in town moving debris, sometimes even bodies. But if you reach a pile of rubble, and there's any evidence of life, what you have to do is pick that pile of rubble brick by brick, glass shard by glass shard.
The story that we've heard time and time again is that of lack of bright lights to continue working through the night.
A part of the tarmac looked like a hospital ward on Friday with patients on drips waiting to be moved out. But that is a tiny proportion.
At an outdoor hospital in town there was not a single doctor or nurse, and people were dying in front of our eyes unnecessarily.
If you have lost a leg or foot and you are lying out in the open at these extraordinary temperatures without water, and medicine, often without any shade for four days, you are not going to live very long.
There is no reason why some of the dozens of doctors who have arrived in the past two days should not go there to treat these people. The roads are clear and it's only a 20-minute drive from the airport.
On Saturday morning, a magnitude-4.5 aftershock struck close to Haiti's capital, the US Geological Survey said, forcing people to flee buildings.
US President Barack Obama met two of his predecessors in the White House, George W Bush and Bill Clinton, to seek their support.
After the talks, Mr Obama said the two men would lead the US' fundraising efforts through the Bush-Clinton Haiti Fund.
"America is moving forward with one of the largest relief efforts in its history," Mr Obama said, warning that recovery would take a long time.
President Bush urged Americans to send "cash", and President Clinton said Haitians "can escape their history and built a better future if we do our part".
US Secretary of State Hillary Clinton is travelling to Haiti on Saturday to assess the damage and convey to the Haitian people "our long term, unwavering support, solidarity and sympathies".
A spokeswoman for the UN Office for the Co-ordination of Humanitarian Affairs said aid workers were dealing with a disaster "like no other" in UN memory because the country had been "decapitated".
"Government buildings have collapsed and we do not even have the support of the local infrastructure," Elisabeth Byrs said in Geneva.
Ms Byrs said the situation was even worse than the devastation wrought by the 2004 tsunami in Indonesia's Aceh province.
"It's worse than the Indonesian earthquake where at least we could get the support of some local authorities," she said.
The whole country has been decapitated
Elisabeth Byrs UN Office for the Co-ordination of Humanitarian Affairs
"To make sure this does not spread, we have taken a number of these people off the streets. We have arrested about 50 people."
There is little police presence in the capital, although some Brazilian UN peacekeepers are patrolling the streets.
UN Undersecretary General for Peacekeeping Alain Le Roy told the US Public Broadcasting Service (PBS) network on Friday: "There have been some incidents where people were looting or fighting for food. They are desperate."
But he added that overall the situation remained under control so far.
The BBC's Nick Davis in Port-au-Prince says the only convoys he has seen are people leaving the city, in search of food, water and medicine.
'Historic effort needed in Haiti'
The UN is reporting a rise in the number of people trying to cross into the neighbouring Dominican Republic, and an influx into Haiti's northern cities.
Overnight the crippled port received its first supply ship since the earthquake, a boat carrying bananas and coal, AFP reports.
Interior Minister Paul Antoine Bien-Aime said 50,000 bodies had been collected, but the total number of dead could be "between 100,000 and 200,000".
The UN said about 300,000 people had been made homeless.
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