It said the storm is now packing maximum wind gusts of 130 mph (210 kilometers), could grow even more and is expected to make landfall later in the day along the Florida Panhandle or Big Bend area as a "life-threatening event".

A storm surge of up to 13 feet (four meters) is expected in some areas, the center said.

Separately, the National Weather Service in the state capital Tallahassee issued a dramatic appeal for people to comply with evacuation orders.

"Hurricane Michael is an unprecedented event and cannot be compared to any of our previous events. Do not risk your life, leave NOW if you were told to do so," it said.