PORT-AU-PRINCE, Haiti -- A frightening new aftershock Wednesday forced more earthquake survivors onto the capital's streets to live and sent others fleeing to the countryside, where aid was only beginning to reach wrecked towns.

A flotilla of rescue vessels, meanwhile, led by the U.S. hospital ship Comfort, converged on Port-au-Prince harbor to help fill gaps in still-lagging global efforts to deliver water, food and medical help.

Hundreds of thousands of survivors of Haiti's cataclysmic earthquake were living in makeshift tents or on blankets and plastic sheets under the tropical sun.

The strongest tremor since the Jan. 12 quake struck at 6:03 a.m., just before sunrise while many still slept. From the teeming plaza near the collapsed presidential palace to a hillside tent city, the 5.9-magnitude aftershock lasted only seconds but panicked thousands of Haitians.

"Jesus!" they cried as rubble tumbled and dust rose anew from government buildings around the plaza. Parents gathered up children and ran.

A slow vibration intensified into side-to-side shaking that lasted about eight seconds, compared to last week's far stronger initial quake that seemed to go on for 30 seconds and registered 7.0 magnitude.

Throngs again sought out small, ramshackle buses to take them away from the city. On Port-au-Prince's beaches, more than 20,000 people looked for boats to carry them down the coast, the local Signal FM radio reported.

But the desperation may be deeper outside the capital, closer to last week's quake epicenter.

"We're waiting for food, for water, for anything," Emmanuel Doris-Cherie, 32, said in Leogane, 25 miles southwest of Port-au-Prince. Homeless in Leogane lived under sheets draped across tree branches, and the damaged hospital "lacks everything," Red Cross surgeon Hassan Nasreddine said.

Hundreds of Canadian soldiers and sailors were deploying to that town and to Jacmel on the south coast to support relief efforts, and the Haitian government sent a plane and an overland team to assess needs in Petit-Goave, a seaside town 10 miles farther west from Leogane that was the epicenter of Wednesday's aftershock.

The death toll was estimated at 200,000, according to Haitian government figures relayed by the European Commission, with 80,000 buried in mass graves. The commission raised its estimate of homeless to 2 million, from 1.5 million, and said 250,000 people need urgent aid.

As of Wednesday the State Department had confirmed the deaths of 33 Americans. The department has opened case files on about 9,000 Americans, based on inquiries into their welfare since the quake.

It said it has positively accounted for about 3,500 of the 9,000. The status of the remaining 5,500 is unknown. About 45,000 Americans were in the country at the time of the quake.

Many badly injured Haitians still awaited lifesaving surgery. "It is like working in a war situation," said Rosa Crestani of Doctors Without Borders at the Choscal Hospital. "We don't have any morphine to manage pain for our patients."

The Comfort, with a medical staff of 550, was anchored in Port-au-Prince harbor and had taken aboard its first two surgical patients by helicopter Tuesday even as it was arriving.

It joined the aircraft carrier Carl Vinson and other U.S. warships offshore, along with the French landing craft Francis Garnier, which carried a medical team, hundreds of tents and other aid.

The seaborne rescue fleet soon will be reinforced by the Spanish ship Castilla, with 50 doctors and 450 troops, and by three other U.S.-based Navy vessels.

Canadian warships were already in Haitian waters, and an Italian aircraft carrier will join the flotilla with medical teams and engineers.

U.N. humanitarian chief John Holmes said it's believed that 3 million people are affected, with 2 million of those needing food for at least six months.

Between the U.N. World Food Program and deliveries by the Red Cross and other private aid groups, about a half-million Haitians should have been reached with "reasonable quantities of food," he said. "That's still very far short of what's needed."

In one sign of normalcy, women carried baskets of cauliflower, sweet potatoes and sugar cane into the city from farms in the hills. Some food and water was on sale in Port-au-Prince's markets, but prices had skyrocketed.

President Rene Preval stressed the relative quiet prevailing over much of Port-au-Prince. People understand, he told French radio, "it is through calmness (and) an even more organized solidarity that we're going to get out of this."