More than 30,000 customers are said to be without power
A homeless man has been killed by a falling tree as Hurricane Hermine rages across Florida with winds of up to 80mph.
The hurricane hit the Florida Gulf coast with heavy lashing rains - causing flooding and blackouts - before weakening to a tropical storm.
The US National Hurricane Centre said Hermine, the fourth hurricane of the 2016 Atlantic season, made landfall over northwest Florida, east of St Marks, at 1.30am local time.
"There is a danger of life-threatening inundation within the next 12 to 24 hours along the Gulf coast of Florida," the NHC said.
Within an hour, 70,000 homes in the state capital Tallahassee and thousands more along the coast were without power.
US media reported toppled trees and downed power lines had left more than 170,000 people without power.
Some residents needed hospital treatment for injuries sustained by high winds knocking down trees onto their homes.
Just under 19 inches of rainfall was recorded near Baskin by the National Weather Service Weather Prediction Centre (NWSWPC).
Storm surges and floods continued to threaten the coastline, as a weakened Hermine moved across Georgia, with winds of up to 60mph.
"The combination of a dangerous storm surge and the tide will continue to cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline," the NHC added.
Georgia Power said more than 30,000 of its customers were without power in and around the cities of Valdosta and Brunswick.
Schools were closed in at least 35 Florida counties and 59 emergency shelters opened across the state following mandatory and voluntary evacuations.
"It is a mess...we have high water in numerous places," Virgil Sandlin, the police chief in Cedar Key, told the Weather Channel.
"I was here in 1985 for Hurricane Elena and I don't recall anything this bad."
Pasco County emergency crews rescued 18 people after their homes were flooded in Green Key and Hudson Beach.
Florida's governor Rick Scott, who declared a state of emergency in 51 out of 67 counties, warned storm surges remained potentially "life-threatening" and urged Gulf Coast residents to take precautions.
He tweeted while all hurricane warnings had been cancelled, "tropical storm warnings are still in effect".
The governors of Georgia and North Carolina also declared emergencies in affected regions.
Hermine is expected to push into the Carolinas and up the East Coast - still carrying with it the threat of heavy rain and flooding.
A tropical storm watch was extended to Sandy Hook, New Jersey - with Hermine expected to be felt over the US Labour Day holiday weekend by communities along the Atlantic Coast.
Hermine is the first hurricane to directly hit the Sunshine State in more than a decade.
The last hurricane to strike Florida was Wilma in 2005, which swept across the Everglades and struck heavily populated south Florida, killing five people.