Port-Au-Prince, Haiti (AP) - Dazed and injured Haitians sat on darkened streets pleading for help Wednesday and untold numbers were trapped in tons of rubble brought down by the strongest earthquake to hit this poor Caribbean nation in more than 200 years.
The extent of destruction from Tuesday afternoon's 7.0-magnitude tremor was far from clear -- and estimating the number of casualties was impossible, save for the dead lying among thousands of collapsed buildings in Haiti's capital.
The ornate National Palace crumbled into itself, the headquarters of the U.N. peacekeeping mission collapsed, and swaths of rickety shacks lay in shambles. Clouds of dust thrown up by falling buildings choked Port-au-Prince for hours.
The United States and other nations began organizing relief efforts, alerting search teams and gathering supplies that will be badly needed in Haiti, the Western Hemisphere's poorest country.
Associated Press journalists found the damage staggering even for a country long accustomed to tragedy and disaster.
Aftershocks rattled the city as women covered in dust clawed out of debris, wailing. Stunned people wandered the streets holding hands. Thousands gathered in public squares long after nightfall, singing hymns.
It was clear tens of thousands lost their homes and many perished in collapsed buildings flimsy and dangerous even under normal conditions.
"The hospitals cannot handle all these victims," Dr. Louis-Gerard Gilles, a former senator, said as he helped survivors. "Haiti needs to pray. We all need to pray together."
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 the poor.
At a destroyed four-story apartment building, a girl of about 16 stood atop a car, trying to peer inside while several men pulled at a foot sticking from rubble. The girl said her family was inside.
U.N. peacekeepers, most of whom are from Brazil, looked for survivors in the ruins of what had been their five-story headquarters. U.N. peacekeeping chief Alain Le Roy said late Tuesday that "as we speak no one has been rescued."
Le Roy said many U.N. personnel were missing, 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.
Much of the National Palace pancaked on 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., centered 10 miles (15 kilometers) west of Port-au-Prince at a depth of just 5 miles (8 kilometers), the U.S. Geological Survey said. USGS geophysicist Kristin Marano called it the strongest earthquake since 1770 in what is now Haiti.
The temblor appeared to have occurred along a strike-slip fault, where one side of a vertical fault slips horizontally past the other, said Tom Jordan, a quake expert at the University of Southern California. The quake's power and proximity to Port-au-Prince likely caused widespread casualties and structural damage, he said.
"It's going to be a real killer," he said.
Most of Haiti's 9 million people are desperately poor, and after years of political instability the country has no real construction standards. In November 2008, following the collapse of a school in Petionville, the mayor of Port-au-Prince estimated about 60 percent of buildings were shoddily built and unsafe in normal circumstances.
Tuesday's quake was felt in the Dominican Republic, which shares the island of Hispaniola with Haiti, but no major damage was reported there. In eastern Cuba, houses shook but no significant damage was reported.
With electricity knocked out in many places and phone service erratic, it was nearly impossible for Haitian or foreign officials to get full details of the devastation.
In Washington, State Department spokesman P.J. Crowley said that U.S. Embassy personnel were "literally in the dark" after power failed.
"They reported structures down. They reported a lot of walls down. They did see a number of bodies in the street and on the sidewalk that had been hit by debris. So clearly, there's going to be serious loss of life in this," he said.
The Diocese of Norwich, Connecticut, said at least two Americans working at its Haitian aid mission were believed trapped in rubble.
"Everybody is just totally, totally freaked out and shaken," said Henry Bahn, a U.S. Department of Agriculture official visiting Port-au-Prince. "The sky is just gray with dust."
President Barack Obama offered prayers for the people of Haiti and said the U.S. stood ready to help. Secretary of State Hillary Rodham Clinton said the U.S. was offering full assistance -- civilian and military -- and a national organization of registered nurses called for nurse volunteers to provide care in Haiti.
Venezuela's government said it would send a military plane with canned foods, medicine and drinking water and provide 50 rescue workers.
Mexico, which suffered an earthquake in 1985 that killed some 10,000 people, planned to send doctors, search and rescue dogs and infrastructure damage experts.
Edwidge Danticat, a Haitian-American author whose books about Haiti have won the National Book Award and the Pushcart Prize, was unable to contact relatives in Haiti. She sat with family and friends at her home in Miami, looking for news on the Internet and watching TV news reports.
"You want to go there, but you just have to wait," she said. "Life is already so fragile in Haiti, and to have this on such a massive scale, it's unimaginable how the country will be able to recover from this."
Associated Press videographer Pierre Richard Luxama in Haiti and AP writers David Koop and Olga R. Rodriguez in Mexico City; David McFadden and Danica Coto in San Juan, Puerto Rico; Matthew Lee in Washington; Alicia Chang in Los Angeles; Andrea Rodriguez in Havana; Tamara Lush in Tampa, Fla.; and Jennifer Kay and Christine Armario in Miami contributed to this report.
The United States and other nations are now organizing relief efforts, alerting search teams and gathering supplies that will be badly needed in Haiti, the Western Hemisphere's poorest country.