Hurricane Earl, which has already struck several islands in the eastern Caribbean, is heading across the Atlantic towards the United States.
Forecasters say it is likely to reach the east coast in the next few days.
Strong winds and torrential rain have buffeted the Virgin Islands and Puerto Rico. Winds of around 200 kilometres an hour are expected to strengthen.
The world’s three largest cruise lines have been forced to re-route several ships to avoid the storm.
The category 4 hurricane – one short of the most powerful – is the second significant storm of this year’s Atlantic season.
Earl is moving west-north-west and curving towards North Carolina. The US National Hurricane Centre says it is too early to say which parts of the east coast might be hit or how much damage is likely to occur.
On its current path the hurricane poses no threat to the major oil and gas installations in the Gulf of Mexico despite earlier fears.
Elsewhere in the Atlantic other tropical storms have also been causing disruption.