A rapidly strengthening Hurricane Irene is heading towards the Bahamas and threatening to become a monster storm.
Irene grew into a Category 2 hurricane late on Monday and the US National Hurricane Centre said it could soon reach Category 3 and possibly become a top-rated Category 4 storm within 72 hours.
"We didn't anticipate it gaining this much strength this early," said a spokesman, adding that the ocean's warm temperatures and the current atmosphere is "very conducive" to energising storms.
Forecasters said it could still be that strong when it slams into the United States, possibly landing in Florida, Georgia, or South Carolina. Irene is expected to rake the Turks and Caicos and the Bahamas today and tomorrow.
Earlier, the storm slashed directly across Puerto Rico, tearing up trees and knocking out power to more than a million people, then headed out to sea north of the Dominican Republic, where its outer bands were buffeting the north coast with dangerous sea surge and downpours.
More than 1,000 Dominicans had to evacuate their homes, with some families in low-lying areas fleeing to churches and public buildings.
Residents earlier had jammed supermarkets and service stations to get supplies. Schools were closed and emergency services were placed on alert. At least 33 flights were cancelled at Santo Domingo's international airport.
The first hurricane of the Atlantic season was a large system that could cause dangerous mudslides and floods in Dominican Republic, the hurricane centre said. It was not expected to make a direct hit on neighbouring Haiti, though that country could still see heavy rain from the storm.