More than 380,000 homes and businesses were without power at the height of the storm.
The tropical storm is located about 30 miles (45 km) south-southwest of Macon, Georgia with maximum sustained winds of 70 miles per hour (115 km per hour), the NHC said in its 12 am EDT position update. By 8pm, it was down to a category 1.
"Michael is likely to produce potentially catastrophic wind damage where the core of the hurricane moves onshore in the Florida Panhandle, and everyone in the hurricane warning area should prepare for life-threatening hurricane winds".
Michael battered the shoreline with sideways rain, powerful gusts and crashing waves, swamping streets and docks, flattening trees, stripped away leaves, shredding awnings and peeling away shingles.
The hurricane strengthened due to the water temperature in the Gulf of Mexico.
Never in recorded weather history has a hurricane hit the mainland United States at such a speed in October, the month marking the end of the June to November hurricane season.
She said: "I'm anxious about my daughter and grandbaby". "It's like a nightmare". How can this happen?
"We are attempting to get to the home".
Power was out in almost 90 percent of Bay County, which includes Panama City, as night fell Wednesday.
"Where homes were, they are not", Ginger Zee, ABC's chief meteorologist, said in a video posted on Twitter. At the time, the then-tropical-storm wasn't expected to achieve its current Category 4 status, but now that it's here, it's time to batten down the hatches. As it moved further inland, its crushing force subsided.
"It's going to be frightful", Thomas told CNN. "Panama City, I don't know if there will be much left". "We will take care of each other".
The storm made landfall northwest of Mexico Beach around noon on Wednesday, with an eye so clear and wide it could easily be seen from space.
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Even before landfall, the hurricane disrupted energy operations in the Gulf, cutting crude oil production by more than 40% and natural gas output by almost a third as offshore platforms were evacuated ahead of the storm's arrival. Coupled with that you have over 145 miles per hour winds. The roar of the winds, he said, sounded like a jet engine.
Mexico Beach is a small tourist town toward the center of Florida's panhandle.
Michael is forecast to move off the Mid-Atlantic coast by early Friday, the NHC said.
"I guess it's the worst-case scenario".
The storm, which caused a major disruption for oil and gas production in the gulf, had the potential to drive sea water levels as high as 14 feet (4.3 meters) above normal in some areas, the National Hurricane Center said.
The NWS said it had found no record of any previous Category 4 hurricanes that made landfall in the Panhandle or the "Big Bend" coastal region. Both were kielled by falling trees as the fierce storm whipped up risky winds. The sinister-looking red and gray skull appeared briefly on the National Oceanic and Atmospheric Administration infrared satellite images.
Scott spoke Wednesday morning with Trump, who signed a pre-landfall emergency declaration Tuesday ensuring that federal resources would be available before and after the storm in the 35 counties where the governor declared a state of emergency. That sort of timetable can make evacuations more hard to manage. Some 17,000 utility restoration workers were also on call.
Briefing Mr Trump, Brock Long, the USA government's disaster chief, said: "This is the most intense hurricane that's struck this area since 1851".
"Hurricane Michael can not break Florida", Scott vowed. Amtrak has also modified its service and is waiving fees for passengers who change their reservations.
Forecasters said it will unleash damaging wind and rain all the way into the Carolinas, still recovering from Hurricane Florence's epic flooding.
Characterized by strong winds and heavy rainfall, the hurricane of 1930 caused severe damage to the Dominican Republic.
By Tuesday, Michael had reached Category 2 strength. A little over a day later, it had transformed into a monster. Hot towers like "hurricane steroids", or "supercharged pistons in the engine". It's large bodies of warm water, scientists say.
Residents of Georgia and Alabama have been hit with power blackouts after the hurricane crossed into the southeastern part of the states.