Hurricane Ike has reached Caribbean islands, bringing winds of 135mph (215km/h), just days after Tropical Storm Hanna caused havoc in the region.
The eye of the storm is "near or over" the Turks and Caicos islands, the US National Hurricane Center (NHC) says.
Ike could dump 12 inches (30cm) of rain in places and cause storm surge flooding of up to 18ft (5.5m) above normal tide levels, the NHC warns.
The hurricane is expected to reach the south-eastern Bahamas later on Sunday.
Extremely dangerous
After weakening on Saturday, Ike regained strength as it approached the islands, and the NHC now describes it as an "extremely dangerous" Category Four hurricane.
Before it reached the islands, the Turks and Caicos' prime minister, Michael Misick, warned residents of the dangers of staying in low-lying areas.
"Ike is an extremely dangerous hurricane," he said.
"Those more vulnerable, those living in low-lying coastal areas should be planning to move soon to shelters or safer locations with family and friends on higher ground," Misick added.
"Anyone intending to remain in low-lying areas will be placing their lives and the lives of others at risk."
After Hanna pummeled the low-lying islands earlier in the week, many residents and visitors have already decided to leave.
Cuba threat
Heading west southwest at about 15mph (24kph), Ike should hit the northern coast of eastern Cuba by late Sunday or early Monday, according to the NHC forecast.
If it stays on its projected course, Ike will cut across the island from east to west, putting the crumbling colonial buildings of the capital, Havana, at risk.
Cuba has issued a hurricane watch for its eastern provinces.
The centre of the hurricane is forecast to pass to the north of Haiti, which shares the island of Hispaniola with the Dominican Republic.
But Haiti, already reeling from three major storms in as many weeks, will not be spared, with up to 12in (30cm) of rain due to fall.
As floodwaters caused by Tropical Storm Hanna receded, Haitian officials said more than 500 people had been killed.
Hurricane Gustav last week and Tropical Storm Fay two weeks ago killed about 120 people.
Hardest hit by Hanna was the city of Gonaives, which was flooded with up to 16ft of water that has only now begun to recede.
Supplies scarce
The devastation there has been described as catastrophic.
Police said 500 people were confirmed dead but that others are still missing and the number could rise higher.
The UN's World Food Program (WFP) said hundreds of thousands of people had been displaced by the flooding.
The WFP has begun distributing food aid but a spokesperson said the scale of the disaster was putting their resources to the test.
Other aid workers say people's spirits are running low after the successive storms.
"Food supplies and water are scarce and the price of the food that's left is rising," said Parnell Denis from Oxfam in Gonaives.
"The morale of people staying in the shelters is so very low; I am afraid to tell them that another storm is on its way."
More bad weather will hamper the aid effort even further.
In the Dominican Republic, which shares the island of Hispaniola with Haiti, there have been no reports of major damage.
However, preparations are under way for the arrival of Hurricane Ike.
"The ground is saturated and some of the dams in the south-east region are fairly close to their maximum capacity," said meteorological official Gloria Ceballos.
Civil defense director Colonel Juan Manuel Mendez said Dominican troops had been put on alert.
PHOTO CAPTION
Hurricane Ike is seen moving across the Atlantic Ocean as Tropical Storm Hanna bears down on the US.
BBC