Hurricane Omar pounded the Virgin Islands and Puerto Rico with lashing rain and 125 mile-per-hour winds on Thursday after strengthening into a major category three storm.

Quickening its pace along a northeasterly track, Omar veered away from San Juan as it headed out to open water with its center about 90 kilometres northwest of Saint Martin at 0700 GMT, the US National Hurricane Center said.

Officials warned of possible fatalities with forecasters saying Omar could rain up to 50 centimetres as it churned across the Northern Leeward Islands and the Virgin Islands.

"These rains could produce life-threatening flash floods and mudslides," read a warning from the NHC.

In Puerto Rico, forecasters lifted a hurricane watch overnight after all commercial flights and public events were canceled and schools and shipping lanes were closed as the island made anxious preparations for the storm.

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

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

Particular areas of concern were the coastlines of Puerto Rico and the Virgin Islands, where massive wave surges of four to 1.2-1.8 metres above normal were predicted.

An oil refinery on Saint 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," spokesperson Alex Moorhead said.

Inspection to be done when possible

The area around the refinery was closed by the US Coast Guard on Tuesday, and would remain shut until further notice, he said. The refinery is owned by Hess Corp. and Venezuela's state oil company, Petroleos de Venezuela.

"Once Hurricane Omar has passed, we will conduct an inspection of our facilities as soon as it is safe to do so. If no damage is found that would impact safe operation of the refinery, the start-up of processing units will begin in sequential order," Moorhead said in a statement.

Hurricane warnings were in effect in the US Virgin Islands and the outlying Puerto Rican islands of Vieques and Culebra, as well as Saint Martin/Marteen, Saba, Saint Eustatius, Saint Barthelemy, the British Virgin Islands and Anguilla.

Saint Martin/Marteen, which is divided between France and the Netherlands, hosts the Caribbean's main air hub after Puerto Rico.

Tropical storm warnings extended to Monserrat, Antigua and Barbuda.

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.

AFP