Washington, Aug 27 (IANS/EFE) Hurricane Irene began to slam the Atlantic coast of the US with heavy rain and ocean swells, with winds of 155 km per hour and the threat of power outages for 65 million people living along the storm's projected path.

Though Irene has downgraded to a Category 2 hurricane and is forecast to continue losing strength, New York Mayor Michael Bloomberg took the step of ordering evacuation of 250,000 people in areas thought vulnerable to flooding.

New York authorities also ordered evacuation of 22 hospitals, clinics and homes for the elderly in areas below sea level.

The public transport system, including buses, subways and surface rail, will also be shut down.

President Barack Obama has warned that the storm could cause large-scale damage alone in the nation's eastern coastline, and consequently asked that everyone take the necessary precautionary measures.

Though hurricanes are an expected occurrence in Florida and the Gulf of Mexico coast, the densely populated mid-Atlantic and Northeast are much less accustomed to - and prepared for - these phenomena.

Authorities issued alerts for almost all the Atlantic coast from North Carolina to Massachusetts, because Irene - which on its path through the Caribbean left six people dead - could cause losses worth millions of dollars in the area's urban centres.

Refineries in Delaware, New Jersey, Pennsylvania and Virginia together process close to eight percent of the fuel in the US, and any interruption caused by Irene could significantly boost prices, analysts said.

North Carolina Governor Beverly Perdue said state patrol, the Red Cross and the National Guard are prepared for any contingency in her state.