Areas along the US East Coast have declared states of emergency as Hurricane Earl churns towards the region.
The hurricane has weakened to a category two storm, with maximum sustained winds of 165km/h (105mph).
US weather officials predicted the storm would continue to weaken as it passed North Carolina and moved towards New England.
But they warned Earl would remain "large and powerful".
Heavy rains were falling on North Carolina's coastal barrier islands late on Thursday, and the storm was expected to turn north-northeast and move up the rest of the East Coast toward New England.
Officials warned that although the storm was declining in strength, it was growing in size.
The storm comes as Americans mark the Labor Day holiday, the traditional end of summer in the US.
"There is still concern that this track, the core of the storm, could shift a little farther to the west and have a very significant impact on the immediate coastline. Our present track keeps it off shore, but you never know," National Hurricane Center (NHC) spokesman Dennis Feltgen said.
The NHC said hurricane-strength winds might be felt as far as 110km (70 miles) from the eye of the storm.
The centre of the storm was approximately 185km south-south east of Cape Hatteras, North Carolina late on Thursday evening, and was moving in a north-easterly direction.
US officials ordered a mandatory evacuation for roughly 35,000 visitors and residents on North Carolina's Ocracoke Island and Hatteras Island on Tuesday.
Both islands are part of North Carolina's Outer Banks, a region popular with tourists.
The local authorities in the Outer Banks expect the storm to pass as close as 88km away from the islands, meaning high winds and waves are likely.
North Carolina's state of emergency authorises the Federal Emergency Management Agency (Fema) and the Department of Homeland Security to head disaster relief efforts.
The North Carolina National Guard is also sending 80 troops to assist with efforts in the region.
Fema has warned people along much of the eastern seaboard of the US to be vigilant and follow official bulletins.
"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, and in eastern Massachusetts.
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.
Officials in North Carolina warned that emergency calls would likely go unanswered when the storm hit the area.
"Once this storm comes in and becomes serious, once it's at its worst point, we are not going to put any emergency worker in harm's way," said North Carolina Governor Beverly Perdue.
On Monday the hurricane battered north-eastern Caribbean islands and Puerto Rico, causing power cuts and flooding.
Earl is being followed by Tropical Storm Fiona, currently north-west of Puerto Rico, and Tropical Storm Gaston, the fourth tropical storm to have formed in the last 11 days.