MIAMI (Reuters) - Hurricane Dean uprooted trees, tore down power lines and ripped the roof off a hospital in St. Lucia on Friday as it raced into the Caribbean on a track that could take it near Jamaica as a dangerously powerful storm next week, officials said.

On the nearby French island of Martinique, sustained winds were measured at 75 mph (120 kph) with gusts up to 105 mph (170 kph), according to France's weather service.

Dean reached the Caribbean Sea through the narrow St. Lucia Channel after a long journey across the Atlantic and threatened to become a powerful Category 4 hurricane on the five-step Saffir-Simpson scale in the area of Mexico's Yucatan Peninsula in four days.

The first hurricane of the Atlantic season lifted the roof off the pediatric wing at Victoria Hospital in St. Lucia's capital, Castries. Patients had been moved from that area and there were no immediate reports of deaths or injuries on the former British colony of 170,000 people, said Dawn French, the island's emergency management director.

"It's very gusty and it's very rainy. We had a dead calm night and now we're getting walloped," said French, reached by telephone as she hunkered down to wait out the storm.

"We seem to have a lot of debris on the roads and some downed trees and downed power lines," she said. "The all-clear hasn't been given so we really haven't been able to get out to look around yet."

By 8 a.m. EDT, Dean was 50 miles west-southwest of Martinique, the U.S. National Hurricane Center said.

It was moving to the west at a brisk 23 mph (37 kph), forecasters said, a speed that would take it well clear of the Lesser Antilles within a few hours.

"I can say it could have been a lot worse. It's not that bad," said Clinton Charlery of Charlery's Car Rental in St. Lucia.