WATCH: Reuters video shows scenes of devastation as rescuers search for earthquake survivors. (Warning: Graphic content. Viewer discretion advised.)
(RFE/RL) -- An international rescue effort is under way in Haiti, where thousands are feared dead after a major earthquake.
The 7.0 earthquake, Haiti's worst in 200 years, caused the collapse of numerous buildings across the Caribbean country.
Schools, hospitals, government buildings, and entire neighborhoods were flattened. President Rene Preval said he believes thousands were killed and a leading senator, Youri Latortue, told The Associated Press that 500,000 could be dead, although he acknowledged that a true count is impossible.
Preval announced that the chief of the UN mission, Hedi Annabi, was killed in the quake.
The international Red Cross said as many as 3 million Haitians -- or one-third of the population -- may need emergency aid and that it would take a day or two for a clear picture of the damage to emerge.
Reports are that all the hospitals in the capital have collapsed or been abandoned as unsafe.
The neighboring island nation of Cuba, which also experienced mild shocks from the quake, has sent 30 doctors and is treating the injured at two field hospitals.
The United States, Britain, Canada, France, Belgium, Sweden, Luxembourg, and the Netherlands were sending reconnaissance and rescue teams, some with search dogs and heavy equipment, while other government and aid groups offered tents, water purification units, doctors, and telecommunications teams.
U.S. Coast Guard and Navy ships began heading to Haiti, and an aircraft carrier carrying helicopters for rescue work should arrive on the afternoon of January 14. The first U.S. civilian aid flights were due to begin landing at the airport this afternoon.
Germany announced it was sending $1,450,000 in immediate aid, and the European Commission has pledged $4.37 million of fast-track funding.
The United Nations said more than 100 of its personnel were unaccounted for after its main headquarters in Port-au-Prince sustained serious damage.
UN peacekeeping chief Alain Le Roy said "less than 10" people have been pulled out, and he could confirm "less than five" deaths.
A UN humanitarian spokeswoman said the main prison in Port-au-Prince had collapsed and there were reports of escaped inmates.
In New York, UN Secretary-General Ban Ki-moon said a major relief effort would be required.
"It is now clear that the earthquake has had a devastating impact on the capital, Port-au-Prince," he said. "The remaining areas of Haiti appear to be largely unaffected. As you are aware, buildings and infrastructure were heavily damaged throughout the capital. Basic services such as water, electricity, have collapsed almost entirely."
The quake, whose epicenter was close to the capital, was followed by powerful aftershocks.
Phone lines to the country failed shortly after the tremor, while roads were blocked by rubble.
Video footage showed scenes of chaos on the streets with people sobbing and appearing dazed amid the rubble.
'Cries Coming Out'
Ian Rodgers, of the organization Save the Children, described the scene shortly afterward to Australia's network Nine.
"You are hearing the grief of people as they realize they've lost people, they can't find their children," Rodgers said. "But then again, you still hearing these cries coming out, people who are rescuing other people from the rubble as somebody comes out alive."
The Red Cross said it would take 24 to 48 hours before a clear picture emerges of the scale of the damage and casualties amid badly damaged communications networks.
In the meantime, a massive international relief effort is getting under way.
The international Red Cross and the UN unlocked emergency funds and mobilized supplies for a "massive" aid operation. Up to 3 million people may have been affected by the quake.
At the White House, U.S. President Barack Obama vowed "unwavering support" to help Haiti recover.
"I have directed my administration to respond with a swift, coordinated, and aggressive effort to save lives," Obama said. "The people of Haiti will have the full support of the United States in the urgent effort to rescue those trapped beneath the rubble and to deliver the humanitarian relief, the food, water, and medicine that Haitians will need in the coming days."
Obama said U.S. rescue teams would arrive in Haiti starting today and through the coming days.
Raymond Joseph, Haiti's ambassador to the United States, said the scope of the damage is still being assessed because the earthquake hit at night:
"We are in the assessment stage, because this earthquake hit us around 10 to 5 last night, about the time it was going to go dark, so people could not assess the damage," Joseph said."We could see what you saw on CNN and on the news, that even the palace, a sturdy building, has partly collapsed."
He said a hospital ship is urgently needed because some of the country's hospitals have collapsed.
Haiti, with a population of some 9 million, is the poorest country in the Western Hemisphere and is ill-equipped to respond to such a disaster.
It borders the Dominican Republic, relatively unscathed but which is now bracing to receive hundreds of injured Haitians injured.