Haiti has been hit by a 5.9-magnitude aftershock, leading to more deaths, damaging several buildings and sending people from the nation's capital fleeing into the streets just over a week after a devastating earthquake.

The country has been hit by a series of aftershocks since last week's 7.0-magnitude quake that has killed at least 200,000 people, with most ranging in magnitude from 4.0 to 5.0, but Wednesday's aftershock has been the strongest.

The U.S. Geological Survey initially reported that the magnitude of the aftershock was 6.1, but they later revised that figure to 5.9.

The USGS said the latest quake was centred 56 kilometres northwest of Port-au-Prince and was 22 kilometres below the surface.

"Some buildings that had been weakened by the original earthquake have been toppled as a result of this one," CBC's David Common reported from Port-au-Prince. "We are told there have been more deaths as a result."

Common said most people had been staying away from buildings, fearing aftershocks could topple them.

Foreign Affairs Minister Lawrence Cannon said the Canadian Embassy was damaged in the aftershock, but no officials were injured.

"This definitely is considered a strong earthquake with the potential to cause some major damage," CBC meteorologist Johanna Wagstaffe said.

She said serious shaking would have been felt up to 200 kilometres away from the epicentre.

Common said the aftershock lasted about 10 seconds.

"I know that in places where people were inside, they quickly moved outside because of this," he said. "It was brief but very strong. We saw that the trees swaying, cars were moving around on the road."

Meanwhile, about 100 surgeons, nurses and medics with the 1st Canadian Field Hospital will deploy to Haiti beginning this weekend, CBC News has confirmed.

The mission will be based in Jacmel, a city of 80,000 near the capital that has an airstrip already in use by the Canadian military. The unit will set up a hospital with an intensive care unit and up to 50 beds. Two surgical teams, including a general and orthopedic surgeon, will oversee the operation.

As donations for Haiti pour in from private citizens around the world, the United States has passed a bill allowing faster tax breaks for U.S. donors.

It would allow donations made by the end of February to be deducted from 2009 returns. So far, Ottawa has not made a similar decision for Canadians who donate to the Haitian relief effort.

Ship sent to remove debris

Speaking in India, U.S. Defence Secretary Robert Gates is sending a ship to Haiti's main port to help remove debris that has blocked the delivery of supplies as the U.S. ramps up its relief efforts in the country.

Gates said the ship would carry cranes and could help get the port back in operation within a week or two.

Relief workers have said the damaged port has prevented large ships from docking and stymied the delivery of food and emergency supplies to victims of last week's earthquake.

Bottlenecks at the damaged harbour and at the capital's airport continue to make it difficult to distribute supplies

About 2,200 U.S. marines have joined 9,000 soldiers who were already on the ground. Helicopters have been dropping food off at distribution points.

The U.S. military had been criticized for its organization of the single-runway airport at Port-au-Prince, with some complaining about how it was prioritizing flights.

But the U.S. air force said Tuesday it had raised the facility's daily capacity to 180 flights, from 30 before the quake.

Meanwhile, Alain Jaffre, a spokesman for the World Food Program, said the UN agency hoped to help 100,000 people by Wednesday.

So far, 250,000 ready-to-eat food rations have been distributed in Haiti. Officials say around three million people are in need. The WFP said it needs to deliver 100 million ready-to-eat rations in the next 30 days.

John Holmes, the UN's humanitarian chief, estimated that about two million Haitians will likely need food aid for six months.

Of the 200,000 believed dead, about 70,000 bodies have been recovered and trucked off to mass graves. Around 250,000 have been injured and 1.5 million left homeless.

But rescue workers are still pulling survivors from the rubble, a week after thousands were killed by the earthquake and days after most experts believed victims could survive.

Around midnight Tuesday, 26-year-old Lozama Hotteline was carried to safety from a collapsed store in the Petionville neighbourhood by the French aid group Rescuers Without Borders.

Earlier that day, Ena Zizi, a 69-year-old ardent Roman Catholic who said she prayed constantly while buried under the rubble, was rescued by a Mexican disaster team.

Doctors who examined Zizi said she was dehydrated and had a dislocated hip and a broken leg.

"I'm all right, sort of," she said.

Experts have said that without water, buried quake victims were unlikely to survive beyond three days.

Zizi said that after the quake, she spoke with a vicar who also was trapped. But after a few days, he fell silent and she spent the rest of the time praying and waiting.

Authorities said close to 100 people had been pulled from wrecked buildings by international search-and-rescue teams.

With files from The Associated Press