The leading edge of Hurricane Michael has hit the Florida coast as an “extremely dangerous” Category 4 storm.

Michael sprang from a weekend tropical depression and grew swiftly into the worst hurricane in recorded history for the north-west coast of Florida, carrying destructive wind, up to a foot of rain and a life-threatening storm surge of up to 13ft.

The sheriff in Panama City’s Bay County issued a shelter-in-place order before dawn on Wednesday, and Florida governor Rick Scott tweeted that for people in the hurricane’s path, “the time to evacuate has come and gone … SEEK REFUGE IMMEDIATELY”.

At 11am local time, Michael had top sustained winds of 145mph and was about 60 miles offshore, moving north-northeast toward Panama City at 14mph.

A satellite image shows Hurricane Michael in the Gulf of Mexico on Tuesday
A satellite image shows Hurricane Michael in the Gulf of Mexico on Tuesday (NOAA via AP)

“We are in new territory,” National Hurricane Centre meteorologist Dennis Feltgen said. “The historical record, going back to 1851, finds no Category 4 hurricane ever hitting the Florida panhandle.”

Only a skeleton staff remained at Tyndall Air Force Base, which is located on a peninsula just south of Panama City.

The home to the 325th Fighter Wing and some 600 military families appeared squarely targeted for the worst of the storm’s fury, and leaders declared “HURCON 1” status, ordering all but essential personnel to evacuate.

The base’s aircraft, which include F-22 Raptors, were flown hundreds of miles away as a precaution, a spokesman said.

A graphic shows the hurricane's path
(PA Graphics)

Ryan Maue of weathermodels.com said: “I guess it’s the worst case scenario. I don’t think anyone would have experienced this in the Panhandle.

“This is going to have structure-damaging winds along the coast and hurricane force winds inland.”

Hurricane preparations
Preparations continue ahead of the hurricane (AP)

The University of Georgia’s Marshall Shepherd, a former president of the American Meteorological Society, called it a “life-altering event” on Facebook and said he watched the storm’s growth on satellite images with growing alarm.

Franklin County sheriff AJ Smith said his deputies had gone door-to-door in some places, urging people to evacuate.

“We have done everything we can as far as getting the word out,” he said. “Hopefully more people will leave.”

On the exposed coast of Florida’s Big Bend, most of the waterfront homes in Keaton Beach stood vacant amid fears of a life-threatening storm surge in an area that had not seen a potentially catastrophic major hurricane in decades.

Mr Scott warned it was a “monstrous hurricane”, while his Democratic opponent for the Senate, Bill Nelson, said a “wall of water” could cause destruction along the Panhandle.

“Don’t think that you can ride this out if you’re in a low-lying area,” Mr Nelson said on CNN.

Mandatory evacuation orders went into effect in Panama City Beach and other low-lying areas in the storm’s path. That included Pensacola Beach but not in Pensacola itself, a city of about 54,000.

Michael could dump up to a foot of rain over some Panhandle communities before its remnants go back out to sea by way of the mid-Atlantic states over the next few days.

Forecasters said it also could bring 3-6in of rain to Georgia, the Carolinas and Virginia, triggering flash flooding in a corner of the country still recovering from Florence.

Isolated tornadoes are also possible.