Residents of mainland Florida are bracing for Hurricane Irma to hit, as conditions in the south of the state deteriorate.
The category four storm with sustained winds up to 130mph (209km/h) moved away from the Florida Keys and should make landfall on the west coast in hours.
High winds and storm surges are affecting the Miami area, but Florida Governor Rick Scott said he was "very concerned" about the west coast.
More than 6.3 million people in Florida were told to evacuate, with warnings of a "life-threatening" storm surge.
Irma has already devastated parts of the Caribbean with at least 27 deaths.
Extreme winds and storm surges continued in the Lower Florida Keys area, which includes Key West.
All residents had been ordered to leave. Some surges could reach 15ft (4.6m).
One official had warned staying on the islands would be "almost like suicide".
Media reports say a man was killed on Saturday in the Keys when his pick-up truck crashed into a tree as the storm gathered pace.
As the eye of the storm is moving north to mainland Florida, more than a million homes in the state are reported to be without power and some 50,000 people have taken refuge in shelters.
Cities such as Tampa and St Petersburg lie in the path of the storm. The Tampa Bay area, with a population of about three million, has not been hit by a major hurricane since 1921.
Governor Scott told NBC's Today Show that though authorities had prepared all week for the arrival of Irma, the prospect of such a large storm surge was "really scary".
Effects are being felt in the Miami area. Miami Beach Police Major Richard Rand told the BBC there was flooding, including 2-3ft inland, and many power lines were down.
In the city of Miami, a crane collapsed onto a building under construction, CBS reported.
Another storm, Jose, further out in the Atlantic behind Irma, is a category four hurricane, with winds of up to 130mph.
It initially followed a similar path to Irma and had threatened several islands already hit by its predecessor, but it has now tracked harmlessly to the north.
Barbuda, whose residents had already left the island as Jose approached, was spared, as were St Martin and St Barthelemy.
Hurricane Katia, in the Gulf of Mexico, a category one storm with winds of up to 75mph, made landfall on the Mexican Gulf coast in the state of Veracruz late on Friday before weakening to a tropical depression.
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