PORT-AU-PRINCE - World leaders pledged aid to rebuild a devastated Haiti, but on the streets of its wrecked capital earthquake survivors were still waiting on Sunday for the basics: food, water and medicine.

Five days after a 7.0 magnitude quake killed up to 200,000 people, international rescue teams were still finding people alive under the rubble of collapsed buildings in Port-au-Prince.

Hundreds of thousands of hungry Haitians were desperately waiting for help, but logistical logjams kept major relief from reaching most victims, many of them sheltering in makeshift camps on streets strewn with debris and decomposing bodies.

In the widespread absence of authority, looters swarmed over collapsed stores on the city's shattered main commercial boulevard, carrying off T-shirts, bags, toys and anything else they could find. Fighting broke out between groups of looters carrying knives, ice-picks, hammers and rocks.

Many Haitians streamed out of the city on foot with suitcases on their heads or jammed in cars to find food and shelter in the countryside, and flee aftershocks and violence.

Many others crowded the airport hoping to get on planes that left packed with Haitians.

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

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, said Obama, flanked at the White House by predecessors George W. Bush and Bill Clinton, who will lead a charity drive to help Haiti.

CHAOS

But on the streets of Port-au-Prince, 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.

And heavily armed gang members who once ran Haiti's largest slum, Cite Soleil, like warlords returned with a vengeance after the quake damaged the National Penitentiary allowing 3,000 inmates to break out.

It's only natural that they would come back here. This has always been their stronghold, said a Haitian police officer in the teeming warren of shacks, alleys and open sewers that is home to more than 300,000 people.

There were jostling scrums for food and water as U.S. military 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.

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.

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.

Looting has been sporadic since Tuesday's earthquake, which flattened large parts of the capital. But it appeared to widen on Saturday as people became more desperate.

The U.N. mission responsible for security in Haiti lost at least 40 of its members when its headquarters collapsed. The United Nations said the mission's chief, Hedi Annabi of Tunisia, his deputy Luiz Carlos da Costa of Brazil and the U.N. police commissioner in Haiti, Doug Coates of Canada, were killed.

MORE RESCUED ALIVE

Aftershocks still shook the capital, terrifying survivors and sending rubble and dust tumbling from buildings.

Dramatizing the need to keep up rescue efforts, three people were pulled out alive from a supermarket early Sunday. U.S. and Turkish teams freed a 7-year-old Haitian girl, a Haitian man and an American woman from the rubble of the five-story building, Reuters photographer Carlos Rawlins said.

They were dazed but did not appear to be seriously injured.

Rescuers had been ready to give up at the site on Saturday, until they were told that a supermarket cashier had managed to call someone in Miami to say she was still alive inside. As many as 100 more people could have been trapped inside the collapsed market.

On Saturday, a Russian team pulled out two Haitian girls still alive -- 9-year-old Olon Remi and 11-year-old Senviol Ovri -- from the ruins of a house.

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

Interior Minister Paul Antoine Bien-Aime said around 50,000 bodies had already been collected and the final death toll will likely be between 100,000 and 200,000.

Dozens of bloated bodies have been 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 makeshift drips hanging from trees.

The weakened Haitian government is in no position to handle the crisis alone. The quake destroyed the presidential palace and knocked out communications and power. President Rene Preval is living and working from the judicial police headquarters.

AIRPORT BOTTLENECK

Hillary Clinton told Haitians the United States will ensure their country emerges stronger and better from the disaster.

We will be here today, tomorrow and for the time ahead, she said after meeting Preval at the airport.

The U.S. State Department confirmed 15 Americans had died in the temblor, including one of its employees in Haiti.

Dozens of countries have sent planes with rescue teams, doctors, tents, food, medicine and other supplies, but faced a bottleneck at Port-au-Prince's small airport.

The American Red Cross said 50-bed field hospitals and water purification equipment that were rerouted to neighboring Dominican Republic arrived by truck convoy, allowing it to start distributing water and first aid in Port-au-Prince.

Air traffic control in Port-au-Prince, hampered by damage to the airport's tower, was taken over by the U.S. military with backup from the nuclear-powered aircraft carrier USS Carl Vinson, which arrived off Haiti on Friday.

Navy helicopters are taking water and rations ashore and ferrying injured people to a field hospital near the airport.

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.

The president of the Inter-American Development Bank, Luis Alberto Moreno, will visit Haiti on Monday and attend a donors meeting in the Dominican Republic to start analyzing Haiti's reconstruction needs, a bank spokesman said.

(Reporting by Tom Brown, Joseph Guyler Delva and Eduardo Munoz in Port-au-Prince, Andrew Quinn in Washington and Patrick Worsnip at the United Nations; writing by Anthony Boadle and Jane Sutton; editing by Eric Beech)