TORONTO — Air Canada is waving flight change fees for almost half a dozen cities in three states as Hurricane Michael beelines for the Florida Panhandle coastline as a Category 4 storm.

Air Canada passengers due to fly in or out of Atlanta, Savannah, Charlotte, Raleigh Durham and Jacksonville today can change their bookings with no change fees as a result of Hurricane Michael.

Major U.S. carriers are waiving change fees for a long list of destinations as well, and cancelling flights.

Hurricane Michael gained strength overnight, with potentially catastrophic winds this morning clocked at 145 mph, making it the most powerful storm on record ever to hit this stretch of Florida coastline, according to reports.

With more than 375,000 people up and down the Gulf Coast warned to clear out, the hurricane’s leading edge began lashing the white-sand shoreline with tropical storm-force winds, rain and rising seas before daybreak, hours before Michael’s centre was expected to blow ashore.

Michael quickly sprang from a weekend tropical depression, reaching Category 4 early this morning as it drew energy from the Gulf of Mexico’s 84 degree waters. That was up from a Category 2 on Tuesday afternoon.

“The time to evacuate has come and gone … SEEK REFUGE IMMEDIATELY,” Florida Gov. Rick Scott tweeted, while the sheriff in Panama City’s Bay County issued a shelter-in-place order before dawn.

As of 8 a.m. this morning Michael was centred about 145 kilometres from Panama City and Apalachicola, moving fast at 21 kph. Tropical storm winds extended 295 kilometres from the centre, and hurricane-force winds reached out 75 kilometres.

Rainfall could reach up to a foot (30 centimetres), and the life-threatening storm surge could swell to 14 feet (4 metres).

The storm appeared to be so powerful – with a central pressure dropping to 933 millibars – that it is expected to remain a hurricane as it moves over Georgia early Thursday. Forecasters said it will unleash damaging winds and rain all the way into the Carolinas, which are still recovering from Hurricane Florence’s flooding.

The historical record, going back to 1851, finds no Category 4 hurricane ever hitting the Florida panhandle.

With files from The Associated Press