PORT-AU-PRINCE, Haiti » A powerful earthquake struck Haiti's capital yesterday with withering force, toppling everything from simple shacks to the ornate National Palace. The dead and injured lay in the streets even as strong aftershocks rippled through the impoverished Caribbean country.

Associated Press journalists based in Port-au-Prince said the damage from the quake—the most powerful to hit Haiti in more than 200 years—is staggering even in a country accustomed to tragedy and disaster. Thousands of people gathered in public squares late into the night, singing hymns and weeping.

Many gravely injured people sat in the streets early today, pleading for doctors. With almost no emergency services to speak of, survivors had few other options.

Thousands of buildings were damaged and destroyed throughout the city, and for hours after the quake the air was filled with a choking dust from the debris of fallen buildings.

The scope of the disaster remained unclear, and even a rough estimate of the number of casualties was impossible. But it was clear from a tour of the capital that tens of thousands of people had lost their homes and that many had perished. Many buildings in Haiti are flimsy and dangerous even under normal conditions.

“;The hospitals cannot handle all these victims,”; said Louis-Gerard Gilles, a doctor and former senator, as he helped survivors. “;Haiti needs to pray. We all need to pray together.”;

In Hawaii, Secretary of State Hillary Rodham Clinton expressed sympathy and pledged support for the victims of yesterday's earthquake in Haiti.

“;We are still gathering information about this catastrophic earthquake,”; she said before giving a speech at the East-West Center in Manoa. “;The United States is offering our full assistance to Haiti and others in the region.

“;We will be offering both civilian and military disaster relief and humanitarian assistance. Our prayers are with the people who have suffered, their families and their loved ones,”; she said.

An Associated Press videographer saw a wrecked hospital where people screamed for help in Petionville, a hillside Port-au-Prince district that is home to many diplomats and wealthy Haitians as well as many poor people.

At a collapsed four-story apartment building, a girl of about 16 stood atop a car, trying to peer inside as several men pulled at a foot sticking out in an attempt to extricate the body. She said her family was inside.

U.N. peacekeepers, most of whom are from Brazil, were trying to rescue survivors from their collapsed five-story headquarters, but U.N. peacekeeping chief Alain Le Roy said late yesterday that “;as we speak no one has been rescued.”;

Many U.N. personnel were missing, he said, including mission chief Hedi Annabi, who was in the building when the quake struck. Some 9,000 peacekeepers have been in Haiti since a 2004 rebellion ousted the president.

Taiwan's Foreign Ministry said its embassy was destroyed and the ambassador hospitalized for undisclosed injuries.

The National Palace crumbled into itself, but Haiti's ambassador to Mexico Robert Manuel said President Rene Preval and his wife survived the earthquake. He had no details.

The 7.0-magnitude quake struck at 4:53 p.m. yesterday, leaving large numbers of people unaccounted for.

Karel Zelenka, a Catholic Relief Services representative in Port-au-Prince, told U.S. colleagues before phone service failed that “;there must be thousands of people dead,”; according to a spokeswoman for the aid group, Sara Fajardo.

State Department spokesman P.J. Crowley said in Washington that U.S. Embassy personnel were “;literally in the dark”; after power failed. The Diocese of Norwich, Conn., said at least two Americans working at its Haitian aid mission were believed trapped in rubble.

With phone service erratic, much of the early communication came from social media such as Twitter. Richard Morse, a musician who manages the famed Olafson Hotel, kept up a stream of dispatches on the aftershocks and damage reports.