A 7.0-magnitude quake – the biggest recorded in this part of the Caribbean – rocked Port-au-Prince last night, collapsing a hospital and sending houses tumbling into ravines.
Witnesses reported seeing bodies in the rubble and clouds of dust shrouding the city, but with telephone communications cut the extent of damage was not immediately clear.
"Everything started shaking, people were screaming, houses started collapsing, it's total chaos," said Joseph Guyler Delva, a Reuters reporter. "I saw people under the rubble, and people killed. People were screaming 'Jesus, Jesus' and running in all directions."
Raymond Joseph, Haiti's ambassador to the US, told CNN from Washington: "I think it is really a catastrophe of major proportions."
The quake, which was shallow, with a depth of just 6.2 miles, struck at 4.53pm local time with the epicentre 10 miles south-west of Port-au-Prince, according to the US Geological Survey. It was said to have lasted around a minute and was quickly followed by two strong aftershocks of 5.9 and 5.5 magnitude. The last major temblor to hit the capital was a magnitude 6.7 in 1984.
The size and proximity to heavily populated slum areas made Tom Jordan, a quake specialist at the University of Southern California, fear the worst. "It's going to be a real killer."