"There must be at least 100,000 people dead and 50.000 buildings destroyed" Sara Fajardo, a spokeswoman for Catholic Relief Services, told the Los Angeles Times. International aid groups are planning a major disaster relief effort. The international Red Cross said up to 3 million people could be affected.
The headquarters of the UN peacekeeping mission in Haiti has collapsed and a large number of UN personnel are missing, according to Alain Le Roy, the head of UN peacekeeping. At least 11 peacekeepers were reportedly killed – eight from China and three from Jordan.
Le Roy told reporters that UN troops, mostly from Brazil, were trying to rescue people from the wreckage of the five-storey building but "as we speak no one has been rescued from this main headquarters".
Gareth Owen, emergencies director at Save the Children, which has about 60 staff in Haiti, said: "We are very concerned about the high likelihood of a significant loss of life because Port-au-Prince is a very densely populated city and the earthquake epicentre was very close to it."
No official estimate of the death toll has been possible but it is clear tens of thousands of people have had their homes destroyed in Port-au-Prince, which has a population of about 1 million, and that many people have perished.
The UN Office for the Co-ordination of Humanitarian Affairs said initial reports suggested "a high number of casualties and widespread damage, with an urgent need for search and rescue".
Location of the Haiti earthquake Dead and injured lay in the streets even as strong aftershocks rippled through the impoverished country. Women covered in dust crawled from the rubble wailing as others wandered through the streets holding hands. Thousands gathered in public squares late into the night singing hymns. There are very few emergency services to speak of and many gravely injured people were still sitting in the streets early this morning, pleading for doctors.
The airport is closed so supplies will probably have to be flown in to neighbouring countries – most likely to the Dominican Republic, which shares the same island.
"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."
With telephone services erratic, much of the early communication came from social media such as Twitter. Richard Morse, a well-known musician who manages the famed Olafson Hotel, kept up a stream of dispatches on the aftershocks and damage reports. Belair, a slum even in the best of times, was said to be "a broken mess".
Raymond Joseph, Haiti's ambassador to the US, told CNN from Washington: "I think it is really a catastrophe of major proportions."
The quake was shallow, with a depth of 6.2 miles, and 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 quake to hit the capital was of magnitude 6.7 in 1984.
The UN secretary general, Ban Ki-moon, said: "My heart goes out to the people of Haiti after this devastating earthquake. At this time of tragedy I am very concerned for the people of Haiti and also for the many United Nations staff who serve there. I am receiving initial reports and following developments closely."
The Pacific tsunami warning centre ruled out a major tsunami but said coasts up to 60 miles away might be affected, prompting alerts in neighbouring Dominican Republic, Cuba and the Bahamas.
Haiti, a former French colony that forms half of the island of Hispaniola, is especially vulnerable to natural disasters. Most of the capital's 3 million people live in hillside slums made of wood, tin and cheap concrete.
"Everybody is just totally, totally freaked out and shaken," said Henry Bahn, a US agriculture official visiting Haiti. "The sky is just grey with dust." He was walking to his hotel room when the ground began to shake. "I just held on and bounced across the wall. I just heard a tremendous amount of noise and shouting and screaming in the distance."
A local employee for the US charity Food for the Poor reported seeing a five-storey building collapse in Port-au-Prince. A colleague said there were more houses destroyed than standing in Delmas Road, a major thoroughfare. Taiwan's foreign ministry said its embassy was destroyed and the ambassador was in hospital with injuries.
The quake crumbled Haiti's presidential residence, the National Palace, but Haiti's ambassador to Mexico, Robert Manuel, said the president, Rene Preval, and his wife had survived. He had no details. Médecins Sans Frontières (MSF) said the quake seriously damaged its 60-bed trauma centre hospital, one of the only free-of-charge surgical facilities in Port-au-Prince.
Another hospital, in Petionville, a wealthy neighbourhood home to diplomats and expatriates, was wrecked..
The US president, Barack Obama, issued a statement sending his "thoughts and prayers". "We are closely monitoring the situation and we stand ready to assist the people of Haiti."
Bill Clinton, the UN's special envoy for Haiti, said his office would do whatever it could to help the country recover and rebuild. "My thoughts and prayers are with the people of Haiti."
The quake was felt in the Dominican Republic, sending people running on to the streets in the capital, Santo Domingo. Houses shook in eastern Cuba but no major damage was reported.
