Tropical Storm Isaac heads to Florida
People in Florida have been feeling the first effects of Tropical Storm Isaac as it nears the US coastline.
After lashing the Florida Keys overnight, Isaac is now heading towards the northern Gulf Coast.
Louisiana, Mississippi and Alabama have followed Florida in declaring states of emergency.
Hundreds of flights have been cancelled and oil and gas production is affected by a storm that has already killed at least nine, including eight in Haiti.
The Republican Party has delayed by a day the start of its convention.
Low-lying areas to the north of the Gulf of Mexico are on flood alert. Some mandatory evacuation orders are in place, says the BBC's Jonny Dymond, in Tampa, Florida.
Alabama Governor Robert Bentley has cancelled his visit to the Republican national convention in the Florida city of Tampa and Louisiana Governor Bobby Jindal may do the same, as they prepare emergency responses in their states.Oil output cut
The National Hurricane Center (NHC) said that at 06:00 GMT on Monday, Isaac was centred about 110 miles (175km) west of Key West, Florida, with wind speeds of 65 mph (105km/h) with some higher gusts, and could reach hurricane force in the next 24 hours.
On Monday, Isaac was expected to move over the eastern Gulf of Mexico, the NHC said.
Fed by the warm waters of the Gulf of Mexico, Isaac is expected to strengthen to a Category 2 hurricane with winds of 105mph (170km/h), and make landfall on Tuesday or Wednesday, somewhere between Florida and Louisiana.
There is also a chance it may hit New Orleans on the seventh anniversary of the devastating Hurricane Katrina.
Isaac is already a large storm and could bring significant damage to areas within 200 miles of its centre.
The Florida Keys have been experiencing rain and strong winds, our correspondent says.
Residents have boarded up windows and put down sandbags.
A steady stream of cars has carried people north along the sole road linking the Keys to the Florida mainland.
Hundreds of flights have been cancelled in and out of Miami, Fort Lauderdale and other southern Florida airports.
The threat of Tropical Storm Isaac has delayed the start of the Republican convention, but you wouldn't know it inside the hall where it will all happen ”
Power cuts have affected communities from Key West to Fort Lauderdale, hitting more than 6,000 customers.
The US Bureau of Safety and Environmental Enforcement says about 24% of the Gulf of Mexico's oil production and 8% of its gas output have been shut off as a precaution.
BP has shut down oil production in the Gulf and is evacuating its platforms there.
Hurricane watches have been put in place along the coastlines of western Florida, Alabama, Mississippi and south-eastern Louisiana.
Florida Governor Rick Scott declared a state of emergency there to make sure emergency services would be ready when the storm hit.
The Republican party has postponed until Tuesday the opening of the convention that will formally nominate Mitt Romney as its presidential candidate
The storm has already caused havoc in the Caribbean, bringing death and considerable damage to Haiti, and floods and downed power lines to Cuba.
Three people were missing in the Dominican Republic, officials said, including the mayor of a town near Santo Domingo, who was later confirmed dead.