Hurricane Michael has become an extremely dangerous Category 4 storm, US experts have warned.

The US National Hurricane Centre said the eye of Michael was about 180 miles south-south-west of Panama City, Florida, at 2am local time (7am BST).

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

Michael is expected to become one of the Florida Panhandle’s worst hurricanes in memory with a life-threatening storm surge of up to 13ft.

Florida officials said roughly 375,000 people up and down the Gulf Coast had been urged or ordered to evacuate.

Evacuations spanned 22 counties from the Florida Panhandle into north central Florida.

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)

Fears remain that some people failed to heed the calls to get out of Michael’s way as the storm began speeding north over the warm waters of the Gulf of Mexico. It is projected to make landfall later on Wednesday.

Meteorologists said it had the potential to become one of the worst storms in the history of the region.

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.

Florida governor Rick Scott warned it was a “monstrous hurricane”, while his Democratic opponent for the Senate, Sen. 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.

Some officials are worried by what they have not seen so far – a rush of evacuees.

“I am not seeing the level of traffic on the roadways that I would expect when we’ve called for the evacuation of 75% of this county,” Bay County Sheriff Tommy Ford said.

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.