The eyewall of Hurricane Ian is now moving onshore to Florida's western coast.
It is expected to bring destructive waves along Englewood to Bonita Beach.
The US National Hurricane Center says the catastrophic storm surge in the area will hit 12 to 18 feet above ground level.
Catastrophic wind damage is also expected.
The latest reported maximum sustained wind speed of Ian is 155 miles per hour, making it a strong Category 4 storm.
Ian is expected to maintain its intensity as it crosses Florida.
The storm will bring heavy rainfall across the Florida peninsula through Thursday, with warnings of life-threatening catastrophic flooding in parts of central Florida.
Heavy rainfall is expected to reach parts of the south-east US later this week.
