Hurricane Irene lashed the Turks and Caicos Islands Tuesday as the category one storm churned on a track that could see it slam the US mainland later in the week.

Forecasters who downgraded Irene, now packing winds of 90 miles (150 kilometers) per hour, said it could still become a major hurricane by Wednesday as it swirls past a series of islands toward the US east coast.

At 2100 GMT, Irene was centered 50 miles (80 kilometers) south-southeast of Grand Turk Island, the Miami-based US National Hurricane Center said.

Fed by warm Atlantic waters, the intensifying storm is expected to whip up ocean storm surges of as high as 13 feet (nearly four meters) by the time it reaches the central Bahamas.

The storm is expected to strengthen to a major hurricane, reaching category three strength by Wednesday, the US National Hurricane Center said.

As Irene churned towards the British overseas territory of Turks and Caicos, authorities closed airports and banks and supermarkets shut their doors. Long lines formed at gas stations in anticipation of the stormy weather.

"The anticipation of the unknown is almost always the worst part of this waiting game," said Tim Ainley, 60, a long-term resident, after moving his handcrafted catamaran to the shelter of a canal.

"I am now preparing my house and getting everything off the floor in case of flooding," he told AFP.

Turks and Caicos spokeswoman Andrea Been said storm surges and high waves would batter the islands later Tuesday and into night time.

In the Dominican Republic, authorities said more than 11,000 people were evacuated to shelter before the storm winds brushed the island's north coast Monday night.

Quake-ravaged Haiti, which shares the island of Hispaniola with the Dominican Republic, was largely spared by the storm, although some mudslides were reported near the northern coast.

Hurricane warnings were however still in effect for parts of the Bahamas, and US officials urged vigilance.

The entire eastern seaboard should be on alert, US officials stressed, with Craig Fugate, chief of the Federal Emergency Management Agency, urging residents to realize that it's "critical that you take this storm seriously."

National Hurricane Center chief Bill Read said a "very large" Irene would likely approach the coast of South Carolina and North Carolina early Saturday.

"But New England could also be in play for a possible impact from Irene," he warned in a media conference call.

Irene is forecast to approach a US mid-Atlantic coast likely to be packed with tourists for one of the final weekends of summer.

And forecasters said that by the time Irene reaches US shores, it is likely to be an even more potent storm -- perhaps as high as a category four on the five-level Saffir-Simpson scale.

"The stakes are high because it would take just a slight shift in the track to the left to make a dramatic change in the impact of the storm in a hugely populated area," said NHC spokesman Dennis Feltgen.

US forecasters said Irene could travel clear up the US Atlantic coast as far north as Delaware by early Sunday.

Up to 10 inches (25 centimeters) of rainfall were expected in the southeastern Bahamas and the Turks and Caicos Islands.

Irene ravaged the US territory of Puerto Rico on Monday, leaving nearly a million people in the dark. Clean-up was underway after Irene downed trees and caused flooding in residential areas.

After the storm hit, US President Barack Obama issued an emergency declaration for the territory.