"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".
At least two deaths have been blamed on the storm.
All told, more than 900,000 homes and businesses in Florida, Alabama, Georgia and the Carolinas were without power.
A fast and furious Hurricane Michael is speeding toward the Florida Panhandle with 120 miles per hour winds and a potential storm surge of 13 feet, giving tens of thousands of people precious little time to get out or board up. Entire roofs were torn away and dropped onto a road. It developed into a hurricane on Monday, and by today, more than 140,000 people were under mandatory evacuation orders.
"I know you just want to go home".
While interests across the Florida Panhandle and Big Bend areas are urged to get out of coastal areas in Hurricane Michael's warning strike zone as the storm of a lifetime bears down for a Category 4 strike Wednesday, another risky situation is developing inland across Georgia, with the storm poised to inflict rare devastation there, as well.
Among those brought to safety were nine people rescued by helicopter from a bathroom of their home in hard-hit Panama City after their roof collapsed, Petty Officer 3rd Class Ronald Hodges said.
"There are so many downed power lines and trees that it's nearly impossible to get through the city", Apalachicola Mayor Van Johnson said.
The storm peeled back part of the gym roof and tore off a wall at Jinks Middle School in Panama City.More news: Trump team asked Israel firm to create election smear campaign
Aluminium siding was shredded and homes were split by fallen trees.
Hundreds of cars had broken windows. As such, he's declared a state of emergency in three dozen counties while ordering evacuations for 10 counties, including Panama City Beach.
Minutes earlier, Michael's eyewall came ashore between Panama City and St. Vincent Island, and the hurricane center warned everyone inside the relative calm of the eye not to venture outside. Gulf Coast Regional Medical Center was treating some, but the hospital evacuated 130 patients as it faced challenges of running on generators after the storm knocked out power, ripped off part of its roof and smashed windows, a spokesman for the hospital's owner HCA Healthcare HCA.N said in an email.
Michael also disrupted energy operations in the U.S. Gulf of Mexico as it approached land, cutting crude oil production by more than 40 percent and natural gas output by almost a third as offshore platforms were evacuated.
Escambia County Sheriff David Morgan bluntly advised residents choosing to ride it out that first-responders won't be able to reach them while Michael smashes into the coast.
In North Carolina's mountains, motorists had to be rescued from cars trapped by high water.
A man outside Tallahassee, Florida, was killed by a falling tree, and an 11-year-old girl in Georgia died when Michael's winds picked up a carport and dropped it on her home, debris striking her in the head. A driver in North Carolina was killed when a tree fell on his vehicle.
More than 375,000 people up and down the Gulf Coast were ordered or urged to clear out as Michael closed in.
The number of people in emergency shelters was expected to swell to 20,000 across five states by Friday, said Brad Kieserman of the American Red Cross.