Haitians piled bodies along the streets of their capital Wednesday after the strongest earthquake to hit the poor Caribbean nation in more than 200 years crushed thousands of structures, from schools and shacks to the National Palace and the United Nations peacekeeping headquarters.

Untold numbers were still trapped. Officials said thousands of people were dead.

The Israeli Foreign Ministry has prepared a 220-member rescue team for departure to the disaster-stricken country, including an elite army corps engineers and a field hospital to assist the casualties.

The military has leased two Boeing 747s of the El Al airline company to transport the team and equipment.

Seven Israelis thought missing were located late Wednesday and early Thursday. One Israeli, the daughter of late peace activist Abie Nathan, was still unaccounter for.

Haitian President Rene Preval said he believed thousands were killed in the quake, and the scope of the destruction prompted other officials to give even higher estimates. Leading Sen. Youri Latortue told The Associated Press that 500,000 could be dead, although he acknowledged that nobody really knows.

Speaking to CNN from the devastated city, Prime Minister Jean-Max Bellerive quantified the number of dead at "well over 100,000." .

In comments to The Miami Herald, Preval described the situation as unimaginable" and said he had had to step over dead bodies himself and could hear the cries of trapped victims, including under the national Parliament building.

"Parliament has collapsed. The tax office has collapsed. Schools have collapsed. Hospitals have collapsed," Preval told the Miami Herald. "There are a lot of schools that have a lot of dead people in them."

"Even the main prison in the capital fell down, and there are reports of escaped inmates," United Nations humanitarian spokeswoman Elisabeth Byrs said in Geneva.

The head of the UN peacekeeping mission was missing and the Roman Catholic archbishop of Port-au-Prince was dead.

The international Red Cross said a third of Haiti's 9 million people may need emergency aid and that it would take a day or two for a clear picture of the damage to emerge.

At first light Wednesday, a U.S. Coast Guard helicopter evacuated four critically injured U.S. Embassy staff to the hospital on the U.S. Naval base at Guantanamo Bay, Cuba, where the military has been detaining suspected terrorists.

President Barack Obama promised an all-out rescue and humanitarian effort, adding that the U.S. commitment to its hemispheric neighbor will be "unwavering."

"We have to be there for them in their hour of need," Obama said.

A small contingent of U.S. ground troops could be on their way soon, although it was unclear whether they would be used for security operations or humanitarian efforts. Gen. Douglas Fraser, commander of the U.S. Southern Command, said roughly 2,000 Marines as part of an expeditionary unit might be deployed aboard a large-deck amphibious ship. Fraser said the ship could provide medical help.

Obama said he has ordered the U.S. government to provide fast, coordinated help to save lives, saying military overflights had already begun assessing damage, emergency supplies were being sent and search and rescue teams would be arriving on Wednesday and Thursday.

"We are just now beginning to learn the extent of the devastation, but the reports and images that we've seen of collapsed hospitals, crumbled homes and men and women carrying their injured neighbors through the streets are truly heart-wrenching," Obama told reporters.

The airport in Port-au-Prince has been closed since the quake hit on Tuesday evening, but Israel decided to send the team with the hope that they would be able to land by the time they arrive.

Israeli ambassador to the Dominican Republic, Amos Radian, is scheduled to join the rescue team whose purpose is to gauge the best way Israel can assist with the crisis and decide on the most immediate needs.

IsraAID also planned to send a 12-man search-and-rescue team, which includes emergency medical staff.

Many will have to help their own staff as well as stricken Haitians. Taiwan's Foreign Ministry said its embassy was destroyed and the ambassador hospitalized. Spain said its embassy was badly damaged.

"Haiti has moved to center of the world's thoughts and the world's compassion," British Prime Minister Gordon Brown said.

"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."

The UN's 9,000 peacekeepers in Haiti, many of whom are from Brazil, were distracted from aid efforts by their own tragedy: Many spent the night hunting for survivors in the ruins of their headquarters.

On Wednesday, The UN said that 17 of its personnel were killed in the quake and that 150 workers were still unaccounted for, including the mission chief.

UN officials said 56 others were injured. "Seven who were seriously hurt were evacuated from the country," they said.

The quake struck at 4:53 P.M., centered 15 kilometers west of Port-au-Prince at a depth of only 8 kilometers, the U.S. Geological Survey said. USGS geophysicist Kristin Marano called it the strongest earthquake since 1770 in what is now Haiti