Floods, devastation after Hurricane Ian hammers Florida

Hurricane Ian inundated cities, turned out the lights on millions of residents and left migrants from an overturned boat missing Thursday as Florida assessed damage from what the state governor described as a "500-year flood event".

Officials launched a major emergency response after one of the most intense US storms in years, with helicopter crews plucking survivors from barrier islands slammed by a deluge that saw storm surges crash through beachfront towns and horizontal rain pound communities for hours.

After an initial look at the breathtaking destruction, Florida Governor Ron DeSantis said the coastal city of Fort Myers and adjacent Cape Coral were "really inundated and really devastated" by the storm.

Video: AFP

He said there were "two unconfirmed fatalities" that were likely linked to the hurricane.

The National Hurricane Center (NHC) downgraded Ian to a tropical storm Thursday, but said it was causing "catastrophic flooding" and forecast further "life-threatening" floods, storm surge and high winds in central and eastern Florida as well as Georgia and South Carolina.

The US Border Patrol said a boat carrying migrants sank at sea during the hurricane, leaving 20 missing.