Michael was a Category 4 hurricane at landfall, with sustained winds of 155 miles per hour (249 km per hour).
The NHC has described Michael as “potentially catastrophic” as the intense Category 4 hurricane is packing top sustained winds of 145mph as it churned towards the Florida Panhandle on today.
An NOAA spokesman said the hurricane had the potential to be “historical” in its impact on the US.
He said: “It’s important to not focus just on the core of the storm.
“This is a huge storm, we are looking at a 200-mile wind spread from the centre so tropical-storm force winds will be pulling out into portions of Alabama, even into portions of central Florida.
This is going to be a devastating storm, possibly historical.”
More than 2.1 million residents across 20 Florida counties are under mandatory or voluntary evacuations.