Hurricane Gonzalo is churning toward Bermuda as a dangerous Category 4 storm, gaining new strength over the open Atlantic as the small British territory rushed final preparations.
The US National Hurricane Center in Miami said Gonzalo reached Category 4 strength during the night.
It was briefly a Category 4 storm on Wednesday before dropping some punch for several hours and then gaining new strength.
Forecasters said fluctuations in intensity are normal for hurricanes.
Early on Thursday, Gonzalo packed top sustained winds of 220km/h with higher gusts and was centred about 865 kilometres south-southwest of Bermuda.
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It was moving toward the north at 15km/h toward Bermuda, where a hurricane warning remains in effect.
The hurricane centre said early on Thursday that the eye of Gonzalo was forecast to pass near Bermuda sometime on Friday.
It added "Gonzalo is expected to be a dangerous hurricane when it moves near Bermuda" even though slow weakening was in the forecast for the storm on Thursday night and Friday.
Forecasters said a dangerous storm surge accompanied by large, destructive waves could cause significant flooding on the island, which has about 103km of shoreline.
About 8 to 15 centimetres of rain was predicted.
The government said it would close the island's international airport on Thursday night, when tropical storm conditions were first expected.
Several airlines increased the number of flights departing from Bermuda ahead of the storm.
Bermuda's residents already were coping with the aftermath of Sunday's Tropical Storm Fay.
More than 1000 homes remained without power and homeowners worked to repair damaged roofs.
The government called out 200 soldiers of the Bermuda Regiment to help with cleanup efforts on the island of roughly 70,000 people.
On Wednesday, the island's hardware stores sold generators, batteries, candles and other items and people picked up free tarpaulins distributed by the government.
Supermarkets and petrol stations braced for more crowds on Thursday.
Bermuda, which is 1400kms east of the US state of South Carolina, has one of the highest per-capita incomes in the world and its strict building codes make structures particularly capable of withstanding storms.
Gonzalo swept by the eastern Caribbean earlier this week, claiming at least one life in the Dutch territory of St Maarten.
