PORT-AU-PRINCE, Haiti - A powerful aftershock sent Haitians screaming into the streets on Wednesday, collapsing buildings, cracking roads and adding to the trauma of a nation stunned by an apocalyptic quake eight days ago.
The magnitude-5.9 jolt matched the strongest of the aftershocks that have followed the huge quake of Jan. 12 that devastated Haiti's capital.
The new temblor collapsed seven buildings in Petit-Goave, the seaside town closest to the epicenter, according to Mike Morton of the U.N. Disaster Assessment and Coordination agency, but there were no reports of people crushed or trapped, perhaps because the earlier quake frightened most people into sleeping outside.
Wails of terror erupted in Port-au-Prince, where the aftershock briefly interrupted rescue efforts amid the broken concrete of collapsed buildings, and prompted doctors and patients to flee the University Hospital.
Hundreds of thousands of Haitians remain homeless, hungry and in mourning - most still waiting for the benefits of a nearly $1 billion global aid campaign that has brought hundreds of doctors and thousands of troops to the impoverished Caribbean nation.
U.N. humanitarian chief John Holmes told reporters in New York that 2 million Haitians will probably need food aid for six months, while the World Food Program and other donors so far have reached only about half a million "with reasonable quantities of food" so far.
The U.S. Navy's floating hospital, USNS Comfort, dropped anchor in view of the capital on Wednesday with about 550 medical staff, joining teams from about 30 other countries trying to treat the injured. About 250,000 people were hurt in the quake and aid groups say many people have died for lack of medical care or adequate equipment.
And the Pentagon announced that 2,000 more U.S. Marines would be sent to Haiti, adding 11,500 U.S. military personnel already on the ground or on ships offshore - a number expected to reach 16,000 by week's end.
At a golf course where U.S. troops have been trying to help 25,000 people living under sheets of plastic and old cloth, soldiers and quake victims alike raced for open ground as the quake began.
A slow vibration intensified into side-to-side shaking that lasted about eight seconds. Some in Port-au-Prince said the far stronger Jan. 12 quake seemed to last for 30 seconds.
"It kind of felt like standing on a board on top of a ball," said Staff Sgt. Steven Payne. The 27-year-old from Jolo, West Virginia, who was part of the U.S. Army's aid mission.
At least one woman died of a heart attack, according to Eddy Thomas, a private undertaker who was wheeling her body along a street in Port-au-Prince: "She had a heart condition, and the new quake finished her."
The U.S. Geological Survey said the aftershock was centered about 35 miles (60 kilometers) west-southwest of Port-au-Prince and 6.2 miles (10 kilometers) below the surface.
It was a little further from the capital than last week's magnitude-7.0 quake, which the killed an estimated 200,000 people and made as many as 2 million homeless, according to the European Union.
Wednesday's temblor matched the strongest of 49 aftershocks of magnitude-4.5 or greater that have followed the Jan. 12 quake and USGS geophysicist Bruce Pressgrave said nobody knows if a still-stronger aftershock is possible.
"Aftershocks sometimes die out very quickly," he said. "In other cases they can go on for weeks, or if we're really unlucky it could go on for months" as the earth adjusts to the new stresses caused by the initial quake.
The shaking ripped 8-inch (20-centimeter) cracks in a road west of the capital near Leogane, where U.S. Marines were setting up a post to aid quake victims who are sleeping in streets, culverts and driveways, often under tree branches draped with sheets to guard against the sun.
The latest quake, combined with a light rain on Tuesday, has complicated rescue efforts, said Dr. Yi Ting Tsai, part of a Taiwanese crew digging for survivors near the ruined cathedral.
"The problem is the rain and the new quake this morning has made the debris more compact," he said.
International aid teams have saved 121 people from the rubble, an unprecedented number, according to aid organization. Dr. Jon Kim Andrus, deputy director for the Pan American Health Organization, said that "countless more have been rescued by Haitians working with no equipment at all," he said.
A 69-year-old domestic worker, Ena Zizi, said she prayed constantly during her week under the rubble.
She had been at a meeting at the residence of Haiti's Roman Catholic archbishop when the Jan. 12 quake struck, trapping her in debris. On Tuesday, a Mexican disaster team pulled her to safety.
Zizi said after the quake, she spoke back and forth with a vicar who also was trapped. But he fell silent after a few days, and she spent the rest of the time praying and waiting.
"I talked only to my boss, God," she said. "I didn't need any more humans."
Doctors who examined Zizi on Tuesday said she was dehydrated and had a dislocated hip and a broken leg.
Elsewhere in the capital, two women were pulled from a destroyed university building. And near midnight Tuesday, a smiling and singing 26-year-old Lozama Hotteline was carried to safety from a collapsed store in the Petionville neighborhood by the French aid group Rescuers Without Borders.
Yet the colossal efforts to help Haiti were proving inadequate because of the scale of the disaster. Expectations exceeded what money, will and military might have been able to achieve.
Governments have pledged nearly $1 billion in aid, and thousands of tons of food and medical supplies have been shipped. But much remains trapped in warehouses, or diverted to the neighboring Dominican Republic. Port-au-Prince's nonfunctioning seaport and many impassable roads complicate efforts to get aid to the people.
Aid is still being turned back from the single-runway airport, where the U.S. military has been criticized by some of poorly prioritizing flights. The U.S. Air Force said it had raised the facility's daily capacity from 30 flights before the quake to 180.
U.S. Defense Secretary Robert Gates said the military will send a port-clearing ship with cranes aboard to Port-au-Prince to remove debris that is preventing many larger aid ships from docking.
The U.N. was sending in reinforcements as well: The Security Council voted Tuesday to add 2,000 peacekeepers to the 7,000 already in Haiti, and 1,500 more police to the 2,100-strong international force.
Perhaps as important for many Haitians was the reopening of several money exchange houses on Wednesday and Haitian banks' announcement that they will reopen in rural provinces on Thursday, then in the capital on Saturday. That will help restore the flow of money from Haitians abroad, who send home $1.9 billion a year.
And they may have something to spend the money on: Farmers are again trudging into the capital from hillside plots balancing packages of cauliflower, sweet potato, sugar cane and lettuce on their heads.