One of the strongest storms in recorded history to hit the US has battered north-west Florida, flooding homes, washing out beaches and snapping trees.
Two people, including a child, were killed by falling debris.
Having weakened to a tropical storm, Michael is on its way to the Carolinas.
Storm-surge warnings are still in place, the US National Hurricane Center says, and residents across the southern US have been warned of the continuing danger from downed powerlines, flash floods and landslides.
There are fears for people who ignored evacuation warnings in some of the areas now flooded.
Hundreds of thousands of homes and businesses were left without electricity in Florida, Alabama and Georgia.
How powerful was Michael when it landed?
Michael made landfall near Mexico Beach, Florida, at around 14:00 (18:00 GMT) on Wednesday.
Unusually warm waters in the Gulf of Mexico turbo-charged the storm from a tropical depression on Sunday.
On Tuesday it was still a category two hurricane but by Wednesday morning it had reached borderline category five, the highest level.
Who are the victims?
Florida officials say a man was killed when he was crushed in an incident involving a tree in Gadsden County.
In Seminole County, Georgia, a metal car-shelter lifted by a gust of wind hit a mobile home, killing a girl of 11.
Travis Brooks, director of Seminole County’s emergency management agency, told ABC News there was “complete and total devastation”.
Michael earlier reportedly killed at least 13 people as it passed through Central America: six in Honduras, four in Nicaragua and three in El Salvador.
How badly was Florida hit?
The storm has knocked out power to more than 900,000 homes and businesses.
More than 370,000 people in Florida were ordered to evacuate but officials believe many ignored the warning.
The coastal city of Apalachicola reported a storm surge of nearly 8ft (2.5m).
“There are so many downed power lines and trees that it’s almost impossible to get through the city,” local mayor Van Johnson was quoted as saying by Reuters news agency.
Florida Governor Rick Scott said the US Coast Guard had carried out 10 missions overnight, saving at least 27 people.
“So many lives have been changed forever,” he told reporters. “So many families have lost everything. This hurricane was an absolute monster.”
Images from Mexico Beach show many homes submerged in water, and there was severe damage to buildings in the state’s Panama City area.
A journalist with the Tampa Bay Times said neighbourhoods in that city “looked like a child’s playroom after a massive tantrum”.
What happens next?
As of early Thursday morning local time, the storm winds had dropped to 60mph, the NHC said.
It warned that communities in north-west Florida and North Carolina faced the threat of life-threatening flooding as rising water moved inland from the coast.
The Carolinas are still recovering from the floods of Hurricane Florence.
States of emergency have been declared in all or parts of Florida, Alabama, Georgia and North Carolina.