* Dazed populace digs for survivors, mass burials start
* Frustrated survivors block roads with corpses
* Troops, doctors, planes full of food head to Haiti (Adds protest with corpses, Coast Guard officer quote)
By Tom Brown and Andrew Cawthorne
PORT-AU-PRINCE, Jan 14 (Reuters) - Desperate Haitians set up roadblocks with corpses in Port-au-Prince on Thursday to demand quicker relief efforts after a massive earthquake killed tens of thousands and left countless others homeless.
Angry survivors staged the protest as international aid began arriving in the Haitian capital to help a nation traumatized by Tuesday's catastrophic earthquake that flattened homes and government buildings.
More than 48 hours after the disaster, tens of thousands of people clamored for food and water and help digging out relatives still missing under the rubble.
Shaul Schwarz, a photographer for TIME magazine, said he saw at least two downtown roadblocks formed with bodies of earthquake victims and rocks.
"They are starting to block the roads with bodies. It's getting ugly out there. People are fed up with getting no help," he told Reuters.
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.
"We have already buried 7,000 in a mass grave," President Rene Preval said.
Planes full of supplies arrived at Port-au-Prince airport faster than crews could unload them and aviation authorities were restricting non-emergency flights.
The influx of aid had yet to reach shellshocked Haitians who wandered the broken streets of Port-au-Prince, searching desperately for water, food and medical help.
Relief workers warned the death toll will rise quickly if tens of thousands of injured Haitians, many with broken bones and serious loss of blood, do not get first aid in the next day or so.
"The next 24 hours will be critical," said U.S. Coast Guard officer Paul Cormier, 54, a qualified emergency worker who runs an orphanage in Haiti and has triaged 300 people since Tuesday's disaster.
OBAMA: "WORLD STANDS WITH YOU"
Looters swarmed a collapsed 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."
Doctors in Haiti, the poorest country in the Western Hemisphere, were ill-equipped to treat the injured.
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. ... America stands with you. The world stands with you," President Barack Obama said.
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 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.
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.
From time to time, aftershocks still shook the wrecked city, sending panicked people running away from buildings.
The quake's epicenter was only 10 miles (16 km) 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 U.N. 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 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 and normal communications were cut off. 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.
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.
For relief effort coverage, go to http://www.alertnet.org/ and for a Haiti timeline see http://link.reuters.com/deb63h. (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 Todd Eastham)
- Reuters - Thomson Reuters Foundation
- For more humanitarian news and analysis, please visit https://www.trust.org/alertnet