PORT-AU-PRINCE (Reuters) - President Barack Obama on Saturday declared one of the largest relief efforts in U.S. history to help Haiti’s earthquake victims as survivors begged for aid still only trickling through to them and looters fought in the streets.

Four days after a massive quake killed up to 200,000 people and wrecked most of the capital Port-au-Prince, hundreds of thousands of Haitians were still desperately waiting for assistance as scavengers and looters preyed on shattered buildings in the widespread absence of authority and order.

Even as aid poured into Port-au-Prince airport on Saturday, thousands of Haitians streamed out on foot with suitcases on their heads or jammed in cars to find food, water and shelter in the countryside and flee aftershocks as well as violence.

Logistical logjams still kept major relief from reaching most victims, many of them sheltering in makeshift camps on streets strewn with debris and decomposing bodies.

On the city’s shattered main commercial boulevard near the port, hundreds of scavengers and looters swarmed over the wrecks of shops, carrying off anything they could find and occasionally fighting among themselves for a prized item.

They carried stones, knives, ice-picks and hammers, as much to defend themselves as to break into wrecked premises and slash open boxes to grab T-shirts, bags, toys and other items.

Obama promised help as U.S. Secretary of State Hillary Clinton flew to Haiti where the shell-shocked government gave the United States control over its main airport to guide aid flights from around the world.

With the government saying up to 200,000 people may have been killed, the quake could be one of the ten deadliest in history.

“We’re moving forward with one of the largest relief efforts in our history to save lives and deliver relief that averts an even larger catastrophe,” Obama said on Saturday, flanked by his predecessors George W. Bush and Bill Clinton who will lead a charity drive to help Haiti.

But on the streets of the city, where scarce police patrols fired occasional shots and tear gas to try to disperse looters, the distribution of aid appeared random, chaotic and minimal. Downtown, young men could be seen carrying pistols.

As international rescue crews combed rubble for survivors across the capital, there were jostling scrums for food and water as U.S. helicopters swooped down to throw out boxes of water bottles and rations. A reporter also saw foreign aid workers tossing packets of food to desperate Haitians.

DISORGANIZED DISTRIBUTION

“The distribution is totally disorganized. They are not identifying the people who need the water. The sick and the old have no chance,” said Estime Pierre Deny, standing at the back of a crowd looking for water with his empty plastic container.

Watching the looters downtown, student Ricardo Fume said: “People have nothing to eat, so they steal these things to sell. The United States had the World Trade Center (the September 11, 2001 terrorist attacks), we had this, it is worse,” Fume said.

Haiti is the Western Hemisphere’s poorest country and has for decades struggled with devastating storms, floods and political unrest. Around 9,000 U.N. peacekeepers have provided security here since a 2004 uprising ousted one president.

On her visit, Hillary Clinton, who brought senior U.S. aid officials with her, embraced Haitian President Rene Preval outside an air-conditioned tent at the Port-au-Prince airport, where she was briefed by Lt. General Ken Keen of the U.S. Southern Command and U.S. Ambassador to Haiti Kenneth Merten.

Her plane brought in supplies and was to return with evacuated Americans.

Even four days after the 7.0 magnitude quake, aftershocks were felt every few hours in the capital, terrifying survivors and sending rubble and dust tumbling from buildings.

Trucks piled with corpses have been ferrying bodies to hurriedly excavated mass graves outside the city, but thousands of bodies still are believed buried under rubble.

U.S. rescuers worked through the night to dig out survivors from one collapsed supermarket where as many as 100 people could have been trapped inside. They were about to give up, when they were told a supermarket cashier had managed to call someone in Miami to say she was still alive inside.

“We have already collected around 50,000 dead bodies,” Interior Minister Paul Antoine Bien-Aime told Reuters. “We anticipate there will be between 100,000 and 200,000 dead in total, although we will never know the exact number.”

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Most dead already collected were buried in mass graves.

LOOTING, FIGHTING FOR FOOD

On the teeming rubble-strewn streets of downtown Port-au-Prince, police were trying to round up looters in the biggest security operation since the earthquake struck.

A Reuters photographer saw police shooting in the air, grabbing and throwing people to the ground, and occasionally kicking detainees in parts of the city. But once the police left, looting and scavenging started again.

Some survivors desperate to receive aid painted sheets with the words in English, “We need assistance for the victims, we need food and water.” Elsewhere, a white-painted wooden sign propped in front of a destroyed building read: “Welcome the U.S. Marines, we need some help, dead bodies inside”.

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Looting had been sporadic since Tuesday’s earthquake, which flattened large parts of the capital. But it appeared to be widening on Saturday as people became more desperate.

The U.N. mission responsible for security in Haiti lost at least 36 of its 9,000 members when its headquarters collapsed. Two top officials are missing.

Dozens of bloated bodies were still dumped in the yard outside the main hospital on Saturday, decomposing in the sun. The hospital gardens were a mass of beds with injured people, with drips hanging from trees and tubes.

The weakened Haitian government was in little position to handle the crisis. The quake destroyed the presidential palace and knocked out communications and power. Preval and Prime Minister Jean-Max Bellerive are living and working in the judicial police headquarters.

AIRPORT BOTTLENECK

Obama said the United States, Brazil, Mexico, Canada, France, Colombia, Russia, Japan, Britain and other countries managed to fly in rescue and logistics personnel and supplies.

Planes and ships arrived with rescue teams, search dogs, tents, water purification units, food, doctors and telecom teams, but faced a bottleneck at the small airport.

“It’s like getting a billiard ball through a straw,” U.S. Vice President Joseph Biden said at a south Florida airbase.

Air traffic control, hampered by damage to the airport’s tower, will be handled by the U.S. military with backup from a nuclear-powered aircraft carrier.

The USS Carl Vinson with 19 helicopters arrived off Haiti on Friday, opening a second significant channel to deliver help. Navy helicopters had begun taking water ashore and ferrying injured people to a field hospital near the airport.

The U.S. military aimed to have 9,000 to 10,000 troops on the ground in Haiti and in ships offshore by Monday.

The Pan American Health Organization said at least eight hospitals and health centers in Port-au-Prince had collapsed or sustained damage and were unable to function.