The centre of Hurricane Irma has hit mainland Florida, just south of Naples, amid warnings of storm surges as high as 15ft (4.5m).
Irma made landfall on Marco Island off Florida’s west coast with winds of up to 120mph (192km/h), but has since been downgraded from category three to two.
More than 3.4 million homes in the state are without power, and parts of the city of Miami are under water.
Three storm-related deaths have been reported, as Irma moves northwards.
In its latest update at 03:00 GMT Monday, the National Hurricane Center (NHC) says “hurricane conditions are continuing across portions of the central Florida peninsula”.
Irma currently has maximum sustained winds of 100mph (160km/h), the NHC says.
The storm was earlier pummelling the area around the city of Fort Myers.
Irma has already devastated parts of the Caribbean, killing at least 28 people.
Some 6.3 million people in Florida had been told to evacuate.
President Donald Trump has approved a major disaster declaration and emergency federal aid for Florida.
He described the hurricane as a “big monster”, praising the federal agencies involved with the storm and saying he would go to the state “very soon”.
“We may have been a little bit lucky in that it went on the west, and it may not have been quite as disruptive, but we’re going to see, it’s going to play out over the next five or six hours,” Mr Trump added.
More : BBC.com