Fearful Haitians fled their putrid quake-hit capital in droves on Saturday as a vast international aid drive struggled to relieve tensions threatening to boil over into riots.

President Barack Obama, speaking alongside former presidents George W. Bush and Bill Clinton at the White House, said the United States was doing its utmost to help. Haitian officials however complained that no one was coordinating the effort.

"At this moment, we're moving forward with one of the largest relief efforts in our history, to save lives and to deliver relief that averts an even larger catastrophe," Obama said.

Four days after the 7.0-magnitude earthquake hit, hopes of finding new survivors faded fast while US troops desperately tried to unblock the aid logjam and Secretary of State Hillary Clinton headed to the disaster zone.

Despite complaints over coordination, vital supplies and medicines were trickling into the poor Caribbean nation after the quake that devastated the capital Port-au-Prince and much of western Haiti.

Hampered by a lack of infrastructure and a Haiti government that admits it is no longer able to function properly, the relief effort has been slow to get into gear while the fate of whole towns and villages remains unclear.

In a sign of growing unease, barricades of burning tires, rubble and human corpses blocked the main road out of the Haitian capital to nearby Carrefour on Saturday as residents called for piles of decomposing bodies to be removed.

"They already took some bodies away, but there are more, many more," said bystander Charles Weber, a 53-year-old voodoo priest, in the crowd of at least three dozen protesters surrounding the smoldering roadblock.

A vanguard of the 10,000 US troops being deployed to Haiti has taken control of the airport, clogged with tons of relief supplies, and has begun the first distribution of aid to quell the threat of violence.

But senior Haitian aid official Michel Chancy complained of "major coordination problems" at the airport, and said that when the planes land, "there is no one in charge."

Tim Callaghan, a regional adviser with the US Agency for International Development, defended the "massive" aid effort and said search and rescue efforts would continue at least until Sunday.

Aid is also being distributed from the USS Carl Vinson, a nuclear-powered aircraft carrier where a fleet of 19 helicopters has carried out limited aid drops.

Many survivors, aware that the already tense situation could quickly deteriorate in a nation prone to violent unrest, refused to wait around for relief and decided to escape the unbearable stench of rotting corpses.

"The streets smell of death," said Talulum Saint Fils, who sold her jewelry for one-way bus tickets for her husband and their four children out of Port-au-Prince.

"I'd go to any place but away from this city," she told AFP. "There is no assistance of any kind, and our children simply cannot live like animals."

The United Nations reported increasing numbers trying to cross the border into neighboring Dominican Republic as well as a surge of quake survivors fleeing into Haiti's northern cities.

"This is a historic disaster. We have never been confronted with such a disaster in the UN memory. It is like no other," Elisabeth Byrs, spokeswoman of the UN Office for the Coordination of Humanitarian Affairs, told AFP in Geneva.

She said a UN team had been to survey the damage in Leogane, west of the capital, and had found 80-90 percent of buildings were damaged or destroyed, with local police estimating up to 10,000 dead in the one town alone.

President Rene Preval, looking exhausted with dark pockets under his eyes, told AFP in an interview late Friday that "the government has lost its capacity to function properly, but it has not collapsed." Related article: Governing Haiti from a police station

As international rescuers worked around the clock in tropical temperatures, battling a lack of fuel and transport, a sense of despair set in among exhausted survivors.

There were also reports of violence and looting, as thousands of criminals escaped from the city's collapsed prison.

Haitian officials said at least 50,000 people had been killed and 1.5 million left homeless in the Caribbean nation, one of the poorest countries in the world, which has long witnessed violence and bloodshed.

UN chief Ban Ki-moon is set to visit Haiti on Sunday after the world body appealed for 562 million dollars from donors.

The UN mission in Haiti (MINUSTAH) was hit hard by the quake, with 37 of its 12,000 employees confirmed dead and some 330 still unaccounted for.

This video was captured by the Associated Press on Jan. 16, 2010.

With AFP.