Surveying the wreckage of his capital city, Haitian President Rene Preval said he thought the death toll would be "unimaginable." Thousands are missing and medical aid is unable to keep up with those who need it most.

Haitian politicians said that thousands of citizens have perished in the massive 7.0-magnitude earthquake that has flattened Port-Au-Prince and plunged the poorest country in the Western Hemisphere into disarray.

From tiny shacks straight up to the presidential palace, very little in the city escaped the devastation.

The first cargo planes with food, water, medical supplies and sniffer dogs headed to the country Wednesday, but officials worried it could be too late for many of those trapped and dying amid the flatten city.

Rescue workers are worried that survivors or those trapped in collapsed buildings may die from exposure or thirst before they can be treated.

Former U.S. president Bill Clinton, the UN Special Envoy to Haiti told CNN "the one thing we are worried about is some people will die from exposure . . . before they can be rescued."

Clinton urged nations to provide helicopters and medical supplies and citizens to donate money to aid organizations.

"Little donations add up to big amounts," he said. "Five or 10 dollars can make a huge difference."

A triage centre was set up in a hotel parking lot, and people with severe injuries moaned under tent-like covers.

"I can't take it any more. My back hurts too much," said Alex Georges, 28, who was still waiting for medical help a day after his school collapsed, killing 11 classmates.

"This is much worse than a hurricane," doctors' assistant Jimitre Coquillon told The Associated Press. "There's no water. There's nothing. Thirsty people are going to die."

About 3,000 police and peacekeepers were on the streets of the capital, clearing debris and directing traffic.

But the law enforcement is thought to be ill-equipped to deal with any major unrest. A CNN reporter said he heard at least a dozen gun shots fired Wednesday night.

The UN's 9,000-member peacekeeping force has patrols on the streets and has secured the airport and port.

Recent developments

• Doctors Without Borders loses three medical facilities in quake
• Canada, U.S., pledge assistance to Haiti
• Prison collapses in Port-au-Prince
• American Red Cross runs out of medical supplies
• 16 UN personnel confirmed dead
• About 150 UN personnel missing
• World Bank to provide $100 million in relief

Haitians pulled dead bodies from the rubble in Port-au-Prince on Wednesday, as they searched for survivors and placed sheet-covered victims at the side of the road. Passerby lifted the sheets to see if their loved ones were underneath. Dust clouds filled the air, the result of buildings that had been levelled in the aftermath of the quake and its aftershocks.

International Red Cross spokesperson Paul Conneally said an estimated three million people -- one-third of the country's entire population -- may need emergency aid, though it will take a day or two for a clear picture of the damage to emerge.

The American Red Cross announced Wednesday afternoon that it ran out of medical supplies, less than 24 hours after the disaster struck.

Preval, believes that thousands may be dead after what is believed to be the worst earthquake to hit Haiti in the past 200 years.

"Parliament has collapsed. The tax office has collapsed. Schools have collapsed. Hospitals have collapsed," President Rene Preval told The Miami Herald. "There are a lot of schools that have a lot of dead people in them."

Some of his colleagues feel the death toll may be even higher.

Haitian Prime Minister Jean-Max Bellerive told CNN he thought the casualty total could be "over 100,000" -- though he gave no basis for his estimate and said he hopes it isn't true. Leading Senator Youri Latortue told The Associated Press that 500,000 could be dead, though he acknowledged that nobody really knows.

World leaders pledged to fast-track assistance to Haiti, with the intention to send aid workers and rescue teams there to assist in a major emergency operation.

The World Bank said it would provide $100 million in aid to Haiti for recovery and reconstruction.

The UN has pledged $10 million in emergency relief funds, and the EU has pledged $4.4 million.

The World Food Program is shipping in 100 tonnes of ready-to-eat meals and energy biscuit from El Salvador.

Supplies are being flown into Port-au-Prince on charter flights from the Dominican Republic.

In Ottawa, Foreign Affairs Minister Lawrence Cannon said Canadian officials worked through the night to deploy Canada's aid resources. A reconnaissance force from the Disaster Assistance Response Team is already en route.

The United States, and countries from Iceland to Venezuela, also pledged their assistance to Haiti.

In Washington, U.S. President Barack Obama called the images coming out of Haiti "truly heart-wrenching."

"Haiti has moved to centre of the world's thoughts and the world's compassion," British Prime Minister Gordon Brown said.

Timeline

The disaster struck Tuesday afternoon, centred about 15 kilometres west of the capital city. U.S. Geological Survey geophysicist Kristin Marano called it the strongest earthquake since 1770 in the area that is now Haiti.

By early Wednesday, casualty reports started to trickle in. Monsignor Joseph Serge Miot, the archbishop of Port-au-Prince, was confirmed to be among the dead and Hedi Annabi, the head of the UN peacekeeping mission, was unaccounted for.

"The cathedral, the archbishop's office, all the big churches, the seminaries have been reduced to rubble," the apostolic envoy to Haiti, the archbishop Bernardito Auza, told the Vatican news agency FIDES.

The headquarters for the UN peacekeeping mission collapsed in Tuesday's disaster, as did the ornate National Palace.

UN peacekeeping chief Alain LeRoy said Annabi was among the missing from the wrecked headquarters. He said only about 10 people had been pulled from the rubble, many of whom were badly injured.

About 150 UN personnel are unaccounted for, the organization said and 16 have been confirmed dead.

The massive quake incapacitated all three Doctors Without Borders medical facilities around the capital. One collapsed completely and the other two were rendered so unstable they had to be abandoned.

The main prison in the capital city also fell, "and there are reports of escaped inmates," said UN humanitarian spokesperson Elisabeth Byrs from Geneva.

Taiwan's Foreign Ministry reported that its embassy in Port-au-Prince had been completely destroyed and the ambassador hospitalized. Spain said its own embassy was badly damaged.

It is believed that tens of thousands have lost their homes as a result of the quake, which Dr. Louis-Gerard Gilles, a former senator, said will leave Haitian hospitals overwhelmed.

"The hospitals cannot handle all these victims," Dr. Louis-Gerard Gilles, a former senator, said as he helped survivors. "Haiti needs to pray. We all need to pray together."

The first quake struck Port-au-Prince at 4:53 p.m. local time on Tuesday. For the next eight hours, a mishmash of sporadic cellphone calls, text messages and pictures posted online formed the early reports on the quake.

It was felt in the Dominican Republic, though no major damage was reported there. Similarly, houses shook in eastern Cuba, though no significant damage was reported.

With files from The Associated Press and The Canadian Press