The hurricane, one of the most powerful hurricanes ever to strike the USA mainland, left at least two people dead.
"We'll have to bulldoze and start over", Linda Marquardt, of Mexico Beach, said of her mud-filled home.
Hurricane Michael is the strongest storm to make landfall in the continental United States in nearly half a century, and the strongest hurricane ever to hit in October.
In Panama City, 20 miles northwest of Mexico Beach, buildings were crushed and boats were scattered around.
Authorities said the state mental hospital in Chattahoochee, which has a section for the criminally insane, was cut off by land, and food and supplies were being flown in.
Mexico Beach, Florida, looked as if a bomb had gone off as residents emerged to tally their losses. Only first responders were allowed in and an 8pm curfew was imposed. Michael left a trail of utility wires on roads, flattened tall pine trees and knocked a steeple from a church.
"The kids live nearby. I've never seen anything like this". "So far, everybody seems to be very safe".
Almost 950,000 homes and businesses were without power in Florida, Alabama, the Carolinas and Georgia on Thursday.
At least 11 people died this week as a result of Michael: an 11-year-old girl in Georgia, four people in Florida, a driver in North Carolina and five people in Virginia, officials said.
Hurricane Michael's violence was visible on Thursday in shattered Florida coastal towns, where rows of homes were ripped from foundations and roofs were peeled off schools by the near-record-force storm blamed for six deaths.