PORT ST JOE, Fla - 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 seven deaths.

Michael smashed into Florida's northwest coast near the small town of Mexico Beach on Wednesday with screeching 155 mile per hour (250 kilometer per hour) winds, pushing a wall of seawater inland.

"The wind was really tearing us apart. It was so scary you’d poo yourself,” said retiree Tom Garcia, 60, who was trapped inside his Mexico Beach home as water poured in to waist height.

He and his partner Cheri Papineau, 50, pushed on their door for an hour to stop the storm surge bursting in as their four dogs sat on top of a bed floating in their home.

Video shot by CNN from a helicopter showed homes closest to the water in Mexico Beach had lost all but their foundations.

A few blocks inland, about half the homes were reduced to piles of wood and siding and those still standing had suffered heavy damage.

Michael, the third most powerful hurricane ever to hit the US mainland, weakened overnight to a tropical storm but marched northeast on Thursday, toppling trees with 50 mph (80 kph) winds and bringing "life threatening" flash flooding to Georgia and Virginia, the National Hurricane Center (NHC)reported.

At least seven people were killed by the storm in Florida, Georgia and North Carolina from falling trees and other hurricane-related incidents, according to state officials.

Gulf Coast Regional Medical Center in hard-hit Panama City, 20 miles (32 km) northwest of Mexico Beach, was treating some of the injured. The hospital was evacuating 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 said in an email.

Much of Port St. Joe, 12 miles (19 km) east of Mexico Beach, was underwater after Michael hit with 155 mph winds, snapping boats in two and hurling a large ship onto the shore, residents said. Only first responders were allowed in and an 8 pm curfew was imposed.