- Clinton says airport reopened for aid flights
* Troops, doctors, planes full of food head to Haiti
* Dazed population digs for survivors
* Looting seen at damaged market
(Adds troops, doctors on the way)
By Tom Brown and Andrew Cawthorne
PORT-AU-PRINCE, Jan 14 (Reuters) - Troops and planeloads of food and medicine headed to Haiti on Thursday to assist traumatized Haitians still rattled by aftershocks from the catastrophic earthquake that flattened homes and government buildings and buried countless people.
Tens of thousands of people were feared dead and many were believed to be still trapped alive in the rubble of the major 7.0 magnitude quake that hit Haiti's capital on Tuesday.
The United States was sending 3,500 soldiers and 300 medical personnel to help with disaster relief and security in the devastated Caribbean capital, with the first of those scheduled to arrive on Thursday. The Pentagon was also sending an aircraft carrier and three amphibious ships, including one that can carry up to 2,000 Marines.
U.S. Secretary of State Hillary Clinton said a U.S. military team had reopened the Port-au-Prince airport so that heavy aircraft could begin bringing in aid.
She pledged long-term U.S. help for the crippled Haitian government. Parliament, the national palace, and many government buildings collapsed and it was unclear how many lawmakers and officials 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," Clinton told CNN.
"We know that there will be tens of thousands of casualties," Clinton added without providing specific numbers on fatalities.
Looters swarmed a broken supermarket in the Delmas area of Port-au-Prince, peacefully carrying out electronics and bags of rice. 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."
There were still no signs of organized rescue operations to free those trapped in debris or remove bodies, and doctors in Haiti, the poorest country in the Western Hemisphere, were ill-equipped to treat the injured.
TREMORS INTERRUPT THE MOURNING
Survivors feared returning to their precarious homes and slept in open areas where groups of women sang traditional religious songs in the dark and prayed for the dead.
"They sing because they want God to do something. They want God to help them. We all do," said Hotel Villa Creole employee Dermene Duma, who lost four relatives.
Foreigners slept around the hotel's pool while scores of injured and dying people lay outside. Sobs and wailing were heard throughout the night but aftershocks interrupted the mourning, sending panicked people running away from the walls.
The quake's epicenter was only 10 miles (16 km) from Port-au-Prince, a sprawling and densely packed city of 4 million people.
Bodies lay all around the hilly city: under rubble, beside roads, being loaded into trucks.
Haitians wandered the chaotic, broken streets of Port-au-Prince, searching desperately for water, food and medical help. Others 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 16 members of its 9,000-strong peacekeeping mission had been killed and scores were still missing. Brazil's army said 14 of its soldiers were among the dead.
SURVIVORS DUG OUT
Haitian President Rene Preval said 30,000 to 50,000 people could have died but did not say where the estimates came from.
Nations around the world pitched in to help. French Foreign Minister Bernard Kouchner said three French state aircraft carrying 40 tonnes of equipment, doctors and security staff had already landed in Haiti and two more were on the way.
The United States, China, and European states were sending reconnaissance and rescue teams, some with search dogs and heavy equipment, while other governments and aid groups offered tents, water purification units, food and telecoms teams.
The influx of aid had yet to reach those struggling to survive because roads were still blocked by rubble and trees, and normal communications were cut off.
OVERWHELMING TASK
U.N. peacekeepers around the city 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."
Haitian Red Cross spokesman Pericles Jean-Baptiste said his organization -- accustomed to dealing with disaster in a country dogged by poverty, catastrophic natural disasters and political instability -- was overwhelmed and out of medicine and body bags.
Many hospitals were too badly damaged to use, and doctors struggled to treat crushed limbs, head wounds and broken bones at makeshift facilities where medical supplies were scarce.
Aid group Doctors Without Borders was sending an inflatable hospital with two operating theaters and capable of housing 100 beds.
(Additional reporting by 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 Bill Trott and Vicki Allen)