Visitors and some residents evacuated from low-lying vacation islands off the North Carolina coast on Wednesday as Hurricane Earl bore down on the U.S. eastern seaboard, churning up dangerous swells.

Earl, still a major Category 3 hurricane, weakened slightly overnight as it barrelled across the Atlantic east of the Bahamas. It was on track to approach North Carolina's coast by early on Friday, the U.S. National Hurricane Centre (NHC) said.

The second major hurricane of the 2010 Atlantic season was packing top sustained winds of 125 mph (205 kph), with hurricane force winds extending outward up to 90 miles (150 km), and tropical storm force winds extending out up to 200 miles (325 km).

While a direct U.S. landfall was not forecast, Earl's swirling winds were expected to sideswipe the densely populated U.S. coast from North Carolina to New England on a forecast northward offshore path during the upcoming U.S. Labour Day holiday weekend marking the end of the summer vacation season.

Earl could bring driving rain, high winds and pounding surf to the U.S. East Coast through Friday and Saturday. NHC spokesman Dennis Feltgen said no storm had threatened such a broad swath of the U.S. shoreline since Hurricane Bob in 1991.

NHC forecasters said a low pressure trough moving eastward off the United States was expected to start turning the hurricane on Thursday, shifting it to the northeast, which should keep it offshore of the U.S. East Coast.

Forecaster Wallace Hogsett said the centre of Earl was expected to pass within 100 miles (160 km) or less of North Carolina's coastal Outer Banks late on Thursday or early on Friday.

We're forecasting it still to be a major hurricane at that time so this is still a serious situation, he said.

OIL REFINERS ON ALERT

U.S. and Canadian East Coast oil refiners said they were monitoring Earl but that it was too early to begin to take any precautionary measures.

Hurricane Earl posed no threat to major U.S. oil and gas installations in the Gulf of Mexico.

At 8 a.m. EST (1 p.m. British time), Earl was moving across the Atlantic well to the east of the Bahamas and was located about 780 miles (1,255 km) south southeast of Cape Hatteras, North Carolina, the Miami-based National Hurricane Centre said.

Large swells from Earl should affect the Bahamas and the southeastern coast of the United States today (Wednesday). These swells will likely cause dangerous surf conditions and rip currents, the centre said.

North Carolina's Dare County ordered the mandatory evacuation of all visitors in Hatteras Island, a popular picturesque vacation spot that draws large numbers of tourists each year. Officials said high waves striking the island could wash over the costal highway, impeding safe travel.

Vacationers and residents were also being evacuated from Ocracoke Island, also on North Carolina's Outer Banks that jut into the Atlantic Ocean.

On Hatteras Island, visitor John Gusciora of Leesburg, Virginia, was reluctant to leave. He had been renting a cottage with three families in the village of Salvo and the weather was sunny on Wednesday, with little to no breeze.

It's disappointing. We've been coming down here for years and this is the best weather we've had until today. Now we have to try to pack up our bags and beat the rush off the island, Gusciora said.

I understand North Carolina washes over really easy. It's sad to go, but it's better to be safe, he added.

A hurricane watch was in effect for most of the North Carolina coast, alerting residents that hurricane conditions -- sustained winds of 74 mph (119 kph) -- were possible within 48 hours.

It was too early to predict how close the hurricane would come to New York when it churned offshore east of the city over the weekend, but emergency officials were recommending that local authorities and residents remain alert.

TROPICAL STORM FIONA

Behind Earl, Tropical Storm Fiona, located about 145 miles (232 km) east of the northern Leeward Islands, strengthened on Wednesday, with winds up to 60 mph (96 kph) as it moved west-northwest, the NHC said.

Fiona was also expected to trek north to northwest in the Atlantic, but steer further east than Earl from the U.S. Atlantic seaboard, and remain a tropical storm at its peak intensity.

Meanwhile, a broad area of low pressure about 800 miles (1,280 km) west-southwest of the Cape Verde Islands in the eastern Atlantic increased in organisation overnight and now had an 80 percent chance of becoming a tropical depression in the next 48 hours.

Early computer models showed that system moving mostly west in the Atlantic on a track that would put it between Barbados and the British Virgin Islands.

On Monday, Earl battered the northeastern Caribbean islands and Puerto Rico, downing power lines, blowing off roofs, toppling trees and causing some flooding.

(Additional reporting by Tom Brown and Pascal Fletcher in Miami, Eileen Moustakis in New York;; Editing by Pascal Fletcher and Will Dunham)

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