Parts of the city of Miami are under water as Hurricane Irma hit mainland Florida, triggering storm surges across the south of the state.
The category four storm with sustained winds up to 130mph (209km/h) moved away from the Florida Keys and made landfall on the west coast.
About 2ft (60cm) of flood water has been seen in the city's financial district, where one major street resembled a river.
More than 1m homes are without power.
More than 6.3 million people in Florida were told to evacuate, with warnings of a "life-threatening" storm surge.
An earlier report said: Irma had 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 said a man was killed on Saturday in the Keys when his pick-up truck crashed into a tree as the storm gathered pace. – agencies