With communications disrupted there were no reports of deaths or injuries soon after the quake, as powerful aftershocks shook the country.
The earthquake had a preliminary magnitude of 7.0 and was centered about 10 miles (15 kilometers) west of the capital of Port-au-Prince, the U.S. Geological Survey said. It had a depth of 5 miles (8 kilometers). It was the largest quake recorded in the area, said USGS analyst Dale Grant, and the last major one since a magnitude-6.7 temblor in 1984.
An Associated Press videographer saw the wrecked hospital in Petionville, a hillside Port-au-Prince district that is home to many diplomats and wealthy Haitians. Elsewhere, a U.S. government official reported seeing houses that had tumbled into a ravine.
Haiti's ambassador to the U.S., Raymond Joseph, said from his Washington office that he spoke to President Rene Preval's chief of staff, Fritz Longchamp, just after the quake hit. He said Longchamp told him that "buildings were crumbling right and left" near the national palace. He said he has not gotten through by phone to Haiti since.
Don Blakeman, an analyst at the USGS in Golden, Colorado, said such a strong quake carried the potential for widespread damage.
"I think we are going to see substantial damage and casualties," he said.
The quake was felt in the Dominican Republic, which shares a border with Haiti on the island of Hispaniola. Some panicked residents in the capital of Santo Domingo fled from their shaking homes.
In eastern Cuba, houses shook but no major damage was immediately reported.
"We felt it very strongly and I would say for a long time. We had time to evacuate," said Monsignor Dionisio Garcia, archbishop of Santiago.
In Haiti, the extent of the damage was unclear.
"Everybody is just totally, totally freaked out and shaken," said Henry Bahn, a U.S. Department of Agriculture official visiting Haiti. "The sky is just gray with dust."
Bahn said he was walking to his hotel room when the ground began to shake.
"I just held on and bounced across the wall," he said. "I just hear a tremendous amount of noise and shouting and screaming in the distance."
Bahn said there were rocks strewn about and he saw a ravine where several homes had stood: "It's just full of collapsed walls and rubble and barbed wire."
The U.S. National Weather Service issued a tsunami watch for Haiti, the Dominican Republic and the Bahamas, but said historically the region has seen few destructive tsunamis.
In Washington, State Department spokesman Gordon Duguid said U.S. officials were holding emergency meetings.
"We need to gather what information we can quickly. We will of course assist in any way we can," he said.
Felix Augustin, Haiti's consul general in New York, said he was concerned about everyone in Haiti, including his relatives.
"Communication is absolutely impossible," he said. "I've been trying to call my ministry and I cannot get through. ... It's mind-boggling."
Associated Press writers David Koop in Mexico City, Matthew Lee in Washington and Andrea Rodriguez in Havana contributed to this report.