MORE NEWS ON TRAGEDY IN HAITI....

PORT-AU-PRINCE - A major earthquake hit impoverished Haiti on Tuesday, toppling buildings in the capital Port-au-Prince, burying residents in rubble and causing many deaths and injuries.

The magnitude 7.0 quake, whose epicentre was inland and only 16 kilometres from the capital Port-au-Prince, sent panic-stricken people screaming into the streets of the city, as a cloud of dust and smoke from falling buildings rose into the sky.

As darkness fell amid scenes of chaos and anguished cries from victims, residents desperately tried to dig out survivors or searched for missing relatives in debris-strewn streets.

A hospital collapsed from the quake, The Associated Press reported. Also, damage was done to an airport and the presidential palace, and a hotel collapsed, Haitian radio reported.

Other government buildings, including the parliament building, and a cathedral in the capital, have also been damaged, according to Agence France-Presse, citing Haitian TV.

There are an estimated 6,000 Canadians living in Haiti, including 700 registered with embassy.

The U.N. also reported that its headquarters suffered serious damage in the quake, and that many of its staff were affected.

"For the moment, a large number of personnel remain unaccounted for," the Under-Secretary-General for Peacekeeping Operations Alain le Roy said in a statement issued in New York.

Some 9,000 U.N. police and troops are stationed there to maintain order. Haiti is the poorest country in the Western Hemisphere and has a history of destructive natural disasters, including being lashed by four hurricanes in a single season in 2008.

The major quake, followed by several aftershocks, prompted a tsunami watch for parts the Caribbean but this was later canceled.

"Everything started shaking, people were screaming, houses started collapsing ... it's total chaos," Reuters reporter Joseph Guyler Delva said in Port-au-Prince.

"I saw people under the rubble, and people killed," he added, saying he had witnessed dozens of casualties.

The international community was quick to stand ready to assist the island country in the immediate aftermath of the quake.

The United States will provide both military and civilian disaster assistance, Secretary of State Hillary Clinton said.

"The United States is offering our full assistance to Haiti and to others in the region. We will be providing both civilian and military disaster relief and humanitarian assistance and our prayers are with the people who have suffered, their families and their loved ones," Clinton said at the start of a speech on Asian relations in Honolulu, Hawaii.

A statement from USAID said they would be sending up to 72 people, six search and rescue dogs and up to 48 tons of rescue equipment to help the victims of the quake.

A local employee for the charity Food for the Poor reported seeing a five-story building collapse in Port-au-Prince, spokeswoman Kathy Skipper told Reuters.

Another Food for the Poor employee said there were more houses destroyed than standing in Delmas Road, a major thoroughfare in the city.

"Within a minute of the quake ... soil, dust and smoke rose up over the city, a blanket that completely covered the city and obscured it for about 20 minutes until the atmospheric conditions dissipated the dust," Mike Godfrey, who works for USAID, told CNN from the city.

The American Red Cross has also pledged $200,000 as an initial investment to assist communities impacted by the quake.

"Initial reports indicate widespread damage in Port au Prince, with continuing aftershocks," Tracy Reines, director of international disaster response for the American Red Cross, said in a release. "As with most earthquakes, we expect to see immediate needs for food, water, temporary shelter, medical services and emotional support."

Even Australia has begun to prepare assistance packages. The government of Queensland has ordered emergency crews to standby, and offered their services should they be required.

"The Queensland Fire and Rescue Service has a special capacity for urban search and rescue," acting emergency services minister Andrew Fraser said in a release. "These resources stand ready and available on request through the national channels to provide assistance."

Experts said the quake's epicentre was very shallow at a depth of only 10 kilometres, which was likely to have magnified the destruction.

Speaking to CNN from Port-au-Prince, Ian Rogers of the charity Save the Children said he could hear cries of anguish and mourning rising up from around the city in the darkness.

Homes and buildings built on hillsides had come crashing down along with earth and rubble.

"All the roads currently are blocked," Rogers said.

"People were screaming 'Jesus, Jesus' and running in all directions," Delva said.

The Hotel Montana in Port-au-Prince, where many foreigners stay, suffered at least some minor damage.

Sailors at the U.S. naval base at Guantanamo Bay in eastern Cuba felt the quake but there was no damage to the base or the detention camp where the United States holds 198 foreign terrorism suspects, said Chief Petty Officer Bill Mesta.

"It just shook a number of the buildings," Mesta said. "It felt like there was a strong gust of wind up against the building."