Michael made landfall on Wednesday afternoon as Category 4 storm, the most powerful to hit Florida's northwestern Panhandle in over 100 yrs.
Florida: Search and rescue teams faced a second day of sifting through the ruined landscape left by Hurricane Michael on Friday as the death toll rose to 11.
After devastating coastal communities in the Florida Panhandle, the remnants of the storm, now downgraded to a post-tropical cyclone, killed five people as it passed through the US state of Virginia.
"Virginia storm updates as of 7.00 am [1100 GMT Friday]. 5 confirmed Michael-related fatalities. 520,000 without power. 1,200 closed roads. 5 suspected tornadoes," the Virginia Department of Emergency Management said on Twitter.
The storm was over the open Atlantic, east of Norfolk, Virginia, early Friday after leveling entire communities on the US Gulf Coast.
In Mexico Beach, a seafront town where the hurricane made landfall, houses had been razed by a storm surge, boats had been tossed into yards and the streets were littered with trees and power lines.
Florida Governor Rick Scott said the storm had caused "unbelievable devastation" and the priority for the moment was looking for survivors among residents who failed to heed orders to evacuate.
"I'm very concerned about our citizens that didn't evacuate and I just hope that, you know, we don't have much loss of life," Scott told ABC.
The US Army said more than 2,000 Florida National Guard soldiers were working on the recovery operations.
Before the latest victims were reported, authorities had recorded four deaths in Florida's Gadsden County, one in Georgia and one in North Carolina.
President Donald Trump pledged to help storm victims.
"Our hearts are with the thousands who have sustained property damage, in many cases entirely wiped out," Trump said. "We will not rest or waver until the job is done and the recovery is complete."
Officials said more than 400,000 homes and businesses were without electricity in Florida and 20,000 utility workers had been deployed to restore power.
Michael made landfall on Wednesday afternoon as a Category 4 storm, the most powerful to hit Florida's northwestern Panhandle in more than a century.
'Houses started floating'
It was downgraded to a tropical storm as it moved through the Carolinas, which are still recovering from last month's Hurricane Florence.
By then, 155 mile (250 kilometer) an hour winds had razed numerous homes from their foundations in Mexico Beach, a town of around 1,000 people, leaving just bare concrete slabs. Other houses were missing roofs or walls. Roads were impassable and canals were choked with debris.
A Mexico Beach resident who rode out the hurricane described the impact of the storm surge to CNN.
"When the water came in houses started floating," said the man identified as Scott. "We had furniture in our house that wasn't even our furniture. The surge had brought stuff in.
"There's nothing left here anymore," he said of the town. "Our lives are gone here. All the stores, all the restaurants, everything.
"It's hard to grasp," he said. "This was never in our imagination."
A storage facility in Panama City Beach housing hundreds of boats was ripped apart by the strong winds with the roof shredding into strips of twisted metal.
Margaret Decambre, 48, rode out the storm in her Panama City fourth-floor condo with her husband and three cats.
"The wind was so hard that it was pushing water through windows and doors," Decambre said. "We had probably about half an inch of water on my floor and no way to stop it from coming in.
"It's total devastation -- no power, no water, no communication," she said.
Decambre said she had opened her home to a friend who takes care of three elderly women.
"We brought all four of them and their cat to my condo," she said. "Yes, it is all about helping others."
Federal Emergency Management Agency (FEMA) chief Brock Long said Michael was the most intense hurricane to strike the Florida Panhandle since record keeping began in 1851.
Long said many Florida buildings were not built to withstand a storm above the strength of a Category 3 hurricane on the five-level Saffir-Simpson Hurricane Wind Scale.