"Ian producing catastrophic flooding over East-Central Florida. Forecast to produce life-threatening flooding, storm surge and gusty winds across portions of Florida, Georgia and the Carolinas," the NHC said in an advisory.
The National Weather Service has issued special weather advisories and warnings for at least nine cities across the region.
As of Thursday morning, the hurricane has left almost 2.6 millions of people without electricity in Florida, the PowerOutage.us web portal said. Another 240,000 customers have experienced power outages in Puerto Rico, while over 15,500 people are without power in Georgia and both Carolinas.
Hurricane Ian has officially made landfall in Florida as a Category 4 storm, the US National Hurricane Center has confirmed.
Hurricane Ian made landfall in Florida on Wednesday. US President Joe Biden declared a "major disaster" in this state.