Hurricane Omar was rapidly losing strength as it headed out to sea Thursday, after pounding the Virgin Islands and Puerto Rico as a ferocious Category Three storm.

At peak strength, Omar packed lashing 200-kilometer per hour (125-mph) winds and drenching rains, but by 1500 GMT maximum sustained winds were around 140 kilometers (85 miles) per hour.

The US National Hurricane Center in Miami said the storm at 1500 GMT was located 180 miles (290 kilometers) northeast of the Northen Leeward Islands, and moving northeast at about 23 miles (37 kilometers) per hour -- a track it was expected to follow for the next two days until it peters out.

Omar sent the US and British Virgin Islands into lock-down after the storm upgraded late Wednesday to a Category Three on the Saffir-Simpson scale of one to five which measures the potential wind damage a hurricane might cause upon landfall.

In Puerto Rico, Omar rendered roads impassable Thursday by flooding, toppled trees and debris, as authorities began the onerous task of cleaning up from the storm.

Officials here reported no loss of life, but said more than 400 people were displaced by Omar and forced to take shelter elsewhere. Meanwhile classes at local schools were suspended for a second day in many localities.

Rescue operators had set up 18 shelters in the island's east which was expected to receive the brunt of the rains and winds.

The storm also lashed the islands of St. Barts and St. Maarten/Martin along with glancing blows on several other nearby islands, including Anguilla, and St. Eustatius.

An oil refinery on St Croix in the US Virgin Islands shut down most of its 500,000 barrels a day operations in advance of the storm, "except those necessary to maintain power supply in the complex," spokesman Alex Moorhead said.

The busy 2008 hurricane season has included devastating Hurricanes Gustav and Ike, which caused millions of dollars in damage in Haiti, Cuba and the United States.

Hurricanes and tropical storms have killed hundreds across the Caribbean and in Mexico, with Haiti -- the poorest nation in the Western hemisphere -- being the worst hit.