Residents walk in floodwaters in the neighborhood of Barquita after days of heavy rain in Santo Domingo, the capital City of the Dominican Republic, Oct 25, 2012. [Photo/Agencies]

NASSAU - Hurricane Sandy pounded the Bahamas with battering winds and rains on Friday, sweeping over the island chain after killing 21 people across the Caribbean and posing a menacing threat to the US East Coast.

Forecasters warned the late-season storm is expected to combine with a polar air mass near the United States next week, potentially producing a highly unusual and potent storm that could wreak havoc along the US East Coast.

Late Thursday, Sandy weakened to a Category 1 storm as it tore though sparsely populated low-lying southeastern islands in the Bahamas, knocking out power and blowing off rooftops of some homes.

Sandy's torrential rains and heavy winds were blamed for the deaths of 21 people. The Cuban government said on Thursday night that 11 people died when the storm barreled across the island, most killed by falling trees or in building collapses in Santiago de Cuba Province and neighboring Guantanamo Province.

Haiti's civil protection office said nine people died even though the country did not suffer a direct hit from Sandy, and one person was killed by falling rocks in Jamaica when the storm struck there on Wednesday.

A Haitian woman walks in heavy rain from Hurricane Sandy in Port-au-Prince, the capital City of Haiti, on Oct 25, 2012. [Photo/Agencies]

The Cuban deaths were an unusually high number for the island country which prides itself on protecting its people from storms by ordering mass evacuations.

Winds and rains generated by Sandy were also being felt in south Florida.  

Early Friday, the US National Hurricane Center said Sandy was about 55 miles (90 km) southeast of Great Abaco Island in the Bahamas and packing maximum sustained winds of 85 miles per hour (140 km per hour).

People walk near to a damaged building in Santiago de Cuba, on Oct 25, 2012. [Photo/Agencies]

Sandy is forecast to remain a Category 1 hurricane as it continues to move over the Bahamas on Friday, sending swirling rains and winds across several hundred miles.

In the Bahamas, government officials warned residents to stay indoors until the storm passed. There were no immediate reports of casualties or serious injuries.

On Long Island, in the southeast corner of the Bahamas island chain, Joel Friese, general manager of the Stella Maris Resort, said Sandy was fierce as it cut across the island on Thursday.

"It was way stronger than we expected," he said by telephone. "There are lots of downed trees and partial to heavy roof damage on some of the buildings."

The Bahamas Electricity Corporation, which supplies power to most of the Bahamas, said Sandy had caused power outages on several islands.