The National Hurricane Center said the storm came ashore near Destin, Florida, at about 8 pm local time (0000GMT) as a Category 2 hurricane before weakening to Category 1, Anadolu agency reported.
More than 610,000 customers were without power in the states of Florida and Alabama, according to PowerOutage.us.
Forecasters warned of a life-threatening storm surge of up to 9 feet (2.7 meters) from the Alabama-Florida border to Grayton Beach, and up to 6 feet (1.8 meters) elsewhere along the Florida Panhandle.
Florida, Georgia, and Alabama declared states of emergency, while the Trump administration approved federal emergency declarations for Florida and Alabama.
Alabama Gov. Kay Ivey ordered tourists and non-residents in parts of Baldwin and Mobile counties to leave immediately. Officials said the evacuation window later closed because winds were too strong.
The storm is expected to weaken to a post-tropical system on Saturday as it moves inland, with rainfall of up to 15 inches (38 centimeters) in some coastal areas and a risk of tornadoes.