PORT-AU-PRINCE Troops and planeloads of food and medicine streamed into Haiti on Thursday to aid a traumatized nation still rattled by aftershocks from the catastrophic earthquake that flattened homes and government buildings and buried countless people.
The Haitian Red Cross said it believed 45,000 to 50,000 people had died and 3 million more -- one third of Haiti's population -- were hurt or left homeless by the major 7.0 magnitude quake that hit its impoverished capital on Tuesday.
The quake flattened buildings across entire hillsides and many people were still trapped alive in the rubble after two days, with little sign of organized rescue efforts. About 1,500 corpses were piled up outside the main hospital and bodies littered many streets.
"We have already buried 7,000 in a mass grave," President Rene Preval said.
Planes full of supplies arrived at the Port-au-Prince airport faster than ground crews could unload them and aviation authorities restricted non-military flights from U.S. airspace for fear planes would run out of fuel while waiting to land.
The influx of aid had yet to reach shell-shocked Haitians who wandered the broken streets of Port-au-Prince, searching desperately for water, food and medical help.
"Money is worth nothing right now, water is the currency," one foreign aid-worker told Reuters.
Looters swarmed a broken supermarket in the Delmas area of Port-au-Prince, carrying out electronics and bags of rice unchallenged. Others siphoned gasoline from a wrecked tanker.
"All the policemen are busy rescuing and burying their own families," said tile factory owner Manuel Deheusch. "They don't have the time to patrol the streets."
British Prime Minister Gordon Brown said Haiti had suffered a tragedy beyond imagination and "must become the center of our world's attention, the world's compassion and the world's humanitarian help."
The United States was sending 3,500 soldiers, 300 medical personnel, several ships and 2,200 Marines. Canadian military ships with 500 personnel were on the way and a disaster aid team had already arrived.
"To the people of Haiti, we say clearly and with conviction, you will not be forsaken. You will not be forgotten. In this, your hour of greatest need, America stands with you. The world stands with you," U.S. President Barack Obama said.
The United States pledged long-term help for the crippled Haitian government. Parliament, the national palace, and many government ministry buildings collapsed and it was unclear how many lawmakers survived. The main prison also fell, allowing dangerous criminals to escape.
"The authorities that existed before the earthquake are not able to fully function. We're going to try to support them as they re-establish authority," U.S. Secretary of State Hillary Clinton told CNN.
There were few signs of organized rescue operations to free those trapped in debris, and doctors in Haiti, the poorest country in the Western Hemisphere, were ill-equipped to treat the injured.
Makeshift tents were strung everywhere and Haitians at one informal camp approached a journalist shouting "water, water" in a multitude of languages.
"Please do anything you can, these people have no water, no food, no medicine, nobody is helping us," said Valery Louis, who organized one of the camps.
Groups of women who slept in the streets overnight sang religious songs in the dark and prayed for the dead. "They want God to help them. We all do," said Hotel Villa Creole employee Dermene Duma, who lost four relatives.
Sobs and wailing erupted each time someone died but aftershocks interrupted the mourning, sending panicked people running away from walls.
The quake's epicenter was only 10 miles from Port-au-Prince, a sprawling and densely packed city of 4 million people in a nation dogged by poverty, catastrophic natural disasters and political instability.
Bodies lay all around the hilly city, and people covered their noses with cloth to try to block the stench. Corpses were delivered by the pickup truck load to the General Hospital in Port-au-Prince, where hospital director Guy LaRoche estimated the bodies piled outside the morgue numbered 1,500.
The Haitian Red Cross had run out of body bags and the International Committee of the Red Cross was sending more.
Haitians clawed at chunks of concrete with bare hands and sledgehammers, trying to free those buried alive.
A 35-year-old Estonian, Tarmo Joveer, was freed from the rubble of the United Nations' five-story headquarters early Thursday, and told journalists he was fine.
The UN said at least 36 members of its 9,000-strong peacekeeping mission had been killed and scores were still missing. Brazil said 14 of its soldiers were among the dead.
Fourteen guests and workers were pulled out alive on Thursday from the landmark Montana Hotel, which was largely flattened. Chilean Army Major Rodrigo Vazquez, who was directing the rescue at that site, said "We estimate 70 more inside ... this is devastating."
Nations around the world pitched in to send rescue teams with search dogs and heavy equipment, helicopters, tents, water purification units, food, doctors and telecoms teams.
Aid distribution was hampered because roads were blocked by rubble and smashed cars, normal communications were cut off and relief agencies' offices were damaged and their staff dead or missing. The port was too badly damaged to handle cargo.
U.N. peacekeepers seemed overwhelmed by the enormity of the recovery task ahead.
"We just don't know what to do," a Chilean peacekeeper said. "You can see how terrible the damage is. We have not been able to get into all the areas."
Many hospitals were too battered to use, and doctors struggled to treat crushed limbs, head wounds and broken bones at makeshift facilities where medical supplies were scarce.
Several nations sent mobile hospitals, surgeons and even psychologists to help traumatized Haitians. The U.S. Navy hospital ship Comfort was on the way back to Haiti, where it delivered medical care after a spate of storms caused massive flooding and mudslides in 2008.
(Additional reporting by Raymond Colitt, Carlos Barria, David Morgan, Joseph Guyler Delva, Stephanie Nebehay, Patrick Worsnip and Louis Charbonneau; Writing by Jane Sutton, Pascal Fletcher and Anthony Boadle; Editing by Vicki Allen, David Storey and Eric Beech)