A powerful earthquake struck Haiti's capital last night with withering force, toppling everything from simple shacks to the ornate National Palace.
The dead and injured lay in the streets as strong aftershocks rippled through the impoverished Caribbean country.
Journalists based in Port-au-Prince said the damage from the quake -- the most powerful to hit Haiti in more than 200 years -- was staggering, even in a country accustomed to tragedy and disaster.
Thousands of people gathered in public squares late into the night, singing hymns and weeping after the 7.0-magnitude quake struck at 4.53pm local time (21.53 GMT).
With almost no emergency services to speak of, many injured people sat in the streets early today, pleading for doctors.
The scope of the disaster remained unclear and even a rough estimate of the number of casualties was impossible.
But it was clear from a tour of the capital that tens of thousands of people had lost their homes and that many had perished.
Many buildings in Haiti are flimsy and dangerous even under normal conditions.
"The hospitals cannot handle all these victims," said Louis-Gerard Gilles, a doctor and former senator, as he helped survivors. "Haiti needs to pray. We all need to pray together."
The headquarters of the 9,000-member Haiti peacekeeping mission and other UN installations were seriously damaged, according to Alain Le Roy, the UN peacekeeping chief in New York. A large number of UN personnel who have been keeping the peace in the country since a 2004 rebellion ousted the president remained unaccounted for.
President Rene Preval and his wife survived the earthquake, according to Robert Manuel, Haiti's ambassador to Mexico.
Karel Zelenka, a Roman Catholic Relief Services representative in Port-au-Prince, told US colleagues before the phone service failed that "there must be thousands of people dead."
"He reported that it was just total disaster and chaos," colleague Sara Fajardo said.
With phone service erratic, much of the early communication came from social media such as Twitter. The news, based mostly on secondhand reports and photos, was disturbing, with people screaming in fear and roads blocked with debris.
The quake appeared to have occurred along a strike-slip fault, where one side of a vertical fault slips horizontally past the other, said earthquake expert Tom Jordan at the University of Southern California.
Most of Haiti's nine million people are desperately poor, and after years of political instability the country has no real construction standards.
It has been estimated that 60pc of the buildings were shoddily built and unsafe in normal circumstances.
President Barack Obama has ordered US officials to start preparing in case humanitarian assistance is needed.