At least 23 people have been reported dead as Hurricane Irma smashed into Cuba and the Bahamas on Saturday.
It was earlier downgraded to a category 4 storm, but has now been upgraded back to a Category 5 storm, striking the Camaguey Archipelago with 160 mph (260 kph) winds.
It is due to hit Florida Keys on Sunday morning, crossing over the entire state over a 30 hour period.
As many as 5.6 million people were told to evacuate from Florida – more than a quarter of the state’s population. At least 540,000 people in parts of Georgia were also told to flee as the storm headed towards the American mainland.
As of 2 a.m. ET, Irma was about 275 miles south-southeast of Miami and moving about 12 mph toward the west, the National Hurricane Center said.
“This is a storm that will kill you if you don’t get out of the way,” said National Hurricane Center meteorologist and spokesman Dennis Feltgen.
Tom Bossert, US homeland security adviser, said: “Please listen to your local authorities.
“You need to evacuate from south to north – that is a staggered and carefully thought-out process. There will come a point where you are on your own.”
As Irma cuts through the Caribbean, two other storms in the region have been upgraded to hurricane status: Katia in the Gulf of Mexico and Jose, which is following Irma in the Atlantic and has made landfall in eastern Mexico.