Coastal residents rushed to board up their homes and stock up on bottled water and other supplies. When a hurricane reaches 157 miles per hour, it is a Category 5, the highest possible.
Michael's barometric pressure at landfall was 919 millibars, by that measurement the third-strongest hurricane to hit the USA on record, trailing on the 1935 Labor Day Hurricane and Hurricane Camille in 1969.
His opponent in Florida's Senate race, Sen.
"So many lives have been changed forever, so many families have lost everything", he said. 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.
Hurricane Michael suddenly became news on Monday after eclipsing its former tropical-storm status while lashing Cuba.
After striking Florida, Michael is forecast to move up the East Coast on Wednesday and Thursday ploughing through the Carolinas, still recovering from Hurricane Florence last month.
An estimated 6,000 people evacuated to emergency shelters, mostly in Florida, and that number was expected to swell to 20,000 across five states by week's end, said Brad Kieserman of the American Red Cross. Authorities were also searching for a boy swept away by a river in Guatemala.
At least 13 people reportedly died in Central America over the weekend as a result of storm rains and floods.
The hurricane also damaged hospitals and nursing homes in the Panama City area, with officials working to evacuate hundreds of patients. Following Hurricane Irma past year, 14 people died when a South Florida nursing home lost power and air conditioning.
"It really started as a tropical storm, and then it went to Category 1, then it was Category 2 and before you know it, it was Category 4", O Shaughnessy said.
"During disasters, Floridians take care of each other", Scott said.
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.
Authorities are anxious about a storm surge that could be as high as 12 feet.
About 3,500 Florida National Guard troops were deployed, along with more than 1,000 search-and-rescue personnel, Governor Scott said.
On its current track, the core of Michael is expected to move northeastward across the southeastern USA on Wednesday night and Thursday, and then move off the Mid-Atlantic coast away from the United States on Friday.
The storm "grew into a monster", Trump said Wednesday from the Oval Office.
In Alabama, Gov. Kay Ivey has placed the entire state under an emergency declaration. Alabama, South Carolina and North Carolina reported more than 160,000 outages.
Michael could also have lingering impact on agriculture in state, officials warned.
With the storm next entering the eastern part of the Gulf of Mexico, which has warm water and favorable atmospheric conditions, "there is a real possibility that Michael will strengthen to a major hurricane before landfall, " Robbie Berg, a hurricane specialist at the Miami-based storm forecasting hub, wrote in an advisory.
Roads were filled with piles of floating debris.
The area is known for its small beach towns, wildlife reserves and the state capital, Tallahassee.
What damage has Michael wrought?
"Today it is about life and safety, " Gillum said.
As the storm closed in on the U.S., it caused havoc in the Caribbean.
Lines at gasoline stations were growing long in Panama City as people prepared to leave areas under mandatory evacuation, Trepanier said.