Tina Susman And Ken Ellingwood Reporting From Mexico City -- Bodies lined the shattered streets and hotels were converted into makeshift hospitals today across Haiti's shattered capital, Port-au-Prince, as the world geared up for a major humanitarian effort in the wake of the earthquake that devastated the desperately poor Caribbean nation.

A day after the 7.0-magnitude quake, rescuers hunted for survivors amid a grim tableau of destruction, with entire hillsides of homes appearing to have tumbled and, in other areas, buildings standing unaffected next to others reduced to piles of dusty debris. Some structures lay in pancake-like concrete heaps.

Homeless or fearful survivors took shelter under tarps across the capital, including the grounds outside the prime minister's office.

The nation's president, Rene Preval, described the destruction as "unimaginable" and predicted the death toll in Tuesday's quake would reach into the thousands. Preval told the Miami Herald that he had stepped over bodies and heard cries from people trapped under the collapsed national Parliament building.

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

Prime Minister Jean-Max Bellerive said a preliminary assessment of the widespread damage led him to fear that the number of dead could be "well over 100,000."

"I hope that's not true," Bellerive told CNN, acknowledging that he had no hard numbers.

The head of the U.N. mission in Haiti and the archbishop of Port-au-Prince were reportedly among the dead as buildings -- including ramshackle shanties, schools and the presidential palace -- suffered astonishing damage. The U.N. reported that the main prison also collapsed and that inmates had escaped.

The earthquake largely knocked out telephone service, hobbling communications from the capital and making it difficult for government officials and relief organizations to measure the full scope of the devastation. Relief workers said it could take a day or two to know how many of Haiti's 9 million residents need assistance.

President Obama promised that the United States would help in any way it could in the worldwide effort to deal with what he called a "cruel and incomprehensible" tragedy.

"This is a time when we are reminded of the common humanity we all share," Obama said in televised remarks from the White House this morning. "With just a few hundred miles of ocean between us, Haitians are our neighbors in the Americas and here at home. We have to be with them in their hour of need."

U.S. officials said most of the damage appeared to be concentrated around Port-au-Prince, a teeming city of 2 million that was already a sprawling slum, with cinder-block shanties packed densely along hillsides and in low-lying areas.

The U.S. military today deployed a 30-person team to assess the damage and help manage the response. U.S. Coast Guard helicopters this morning evacuated four severely injured U.S. embassy employees to the Navy base in Guantanamo, Cuba. About 45,000 U.S. citizens live in Haiti, but officials said they had heard no reports so far of widespread casualties among them.

Gen. Douglas Fraser, commander of the U.S. Southern Command, said as many as 2,000 Marines could soon be sent to Haiti to provide aid and help keep law and order. The military's immediate goals are to help restore telecommunications and get the city's damaged airport up and running, Fraser told reporters in Washington. The airport is reported to be usable but the control tower was badly damaged, prompting commercial airlines to cancel flights to and from Port-au-Prince.

Haiti's ambassador to the U.S., Raymond Joseph, appealed early today for medical help and rescue specialists. He said the country was in urgent need of a hospital ship and rescue personnel.

Joseph said many government ministry buildings had collapsed and that the presidential palace, a graceful white French colonial structure, was damaged.

"It's a major catastrophe," he told reporters at the Haitian Embassy in Washington.

But Joseph said the "silver lining" was that the earthquake struck shortly before 5 p.m., when many office workers had gone home for the day, probably reducing the number of fatalities.

The body of Archbishop Joseph Serge Miot was found in the ruins of his office, the Rev. Pierre Le Beller of the Saint Jacques Missionary Center in Landivisiau, France, told the Associated Press by telephone. He said that fellow missionaries in Haiti had told him they found Miot's body.