The hurricane is currently heading north-west Evacuations have begun in areas of the US east coast likely to be hit by Hurricane Earl.
The storm has dropped to category three but is still generating sustained winds of 201km/h (135mph).
President Barack Obama said officials needed to be ready for a “worst case” scenario in a call to the US Federal Emergency Management Agency (Fema).
One island in North Carolina’s Outer Banks is being evacuated and visitors are being asked to leave another.
“The most important thing for people living in Earl’s potential tract to do is to listen to and follow the instructions of their local officials”
Craig Fugate Fema administratorIn pictures: Hurricane Earl batters Caribbean
The narrow islands are served by a single main road and officials worry that waves washing over it will cause danger to travellers.
Fema has warned people along much of the the eastern seaboard of the US to be vigilant and follow official bulletins.
Forecasters at the National Hurricane Center said they expected the hurricane to turn north and then run parallel to the east coast.
“The most important thing for people living in Earl’s potential tract to do is to listen to and follow the instructions of their local officials,” Fema administrator Craig Fugate said.
A hurricane warning has been issued for the east coast of the US from Bogue Inlet North Carolina north-eastward to the North Carolina/Virginia border, including the Pamlico and Albemarle sounds.
The hurricane watch has been adjusted northward and now extends from the North Carolina/Virginia border northward to Cape Henlopen, Delaware.
A warning means hurricane conditions are expected somewhere within the affected area, with the first tropical storm-force winds within 36 hours. A watch expects the same within 48 hours.
The local authorities in the Outer Banks expect the storm to pass 80 miles (130km) away from the islands, which are popular with tourists, meaning high winds and waves are likely.
Ferries have been transporting vehicles from Hatteras Island as part of the evacuation Hatteras Island is being evacuated of visitors, while both visitors and residents have been told to leave Ocracoke Island just to the south.
The hurricane is currently east of the central Bahamas and is moving north-west.
“Large swells from Earl should affect the Bahamas and the south-eastern coast of the United States today [Wednesday]. These swells will likely cause dangerous surf conditions and rip currents,” the NHC said.
The Labor Day weekend marks the end of a holiday season and many Americans use it to head for the beach.
On Monday the hurricane battered north-eastern Caribbean islands and Puerto Rico, causing power cuts and flooding.
Earl is being closely followed by Tropical Storm Fiona, currently east of the Leeward Isles with winds of up to 65km/h.
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