Powerful Hurricane Michael was hours away from smashing into Florida's northwestern shore on Wednesday with a wall of water and roof-shredding winds, and the state's governor said it would be the worst hurricane to hit the region in a century.

Authorities told residents along the affected areas of Florida's Gulf of Mexico coast that they had run out of time to evacuate and should hunker down.

A very dangerous Category 4 storm on five-step Saffir-Simpson scale, Michael strengthened as it moved north over the Gulf of Mexico and by 8 a.m. ET (1200 GMT) was carrying top winds of 145 miles per hour (230 km per hour), the National Hurricane Center said.

Joe Durant tweet

The hurricane was set to make landfall later on Wednesday on Florida's Panhandle and could drive sea water levels as high as 14 feet (4.3 meters) above normal in some areas, the center said. The storm could strengthen further before coming ashore, it said.

More than 2.1 million residents of at least 20 Florida counties were under mandatory or voluntary evacuation orders. Much of this part of Florida is rural areas known for small tourist cities, beaches, wildlife reserves and Tallahassee, the state capital.

The Weather Channel tweet

"Hurricane Michael is forecast to be the most destructive hurricane to hit the Florida Panhandle in a century," Governor Rick Scott told reporters, speaking about seven hours before Michael was expected to make landfall.

Earlier, Scott said on Twitter that it was too late to evacuate the target zone and that people who had stayed should immediately seek refuge.

Some of the storm's most significant early impact was to offshore energy production. U.S. producers in the Gulf cut oil production by about 40 percent and natural gas output by 28 percent on Tuesday, the Bureau of Safety and Environmental Enforcement said.

President Donald Trump declared a state of emergency for the entire state of Florida, freeing up federal assistance to supplement state and local disaster responses.

Apalachicola Mayor Van Johnson said the city, which could suffer some of the worst of the storm surge, was under mandatory evacuation orders.

National Hurricane Center tweet

"My greatest concern is that some people are just now starting to take this storm seriously and are evacuating," he told CNN. And I just hope the others that have not made that decision get out while the roads are still passable and before the bridges close."

The storm was heading north at 13 mph (20 kph) and was about 90 miles (145 km) southwest of Panama City, Florida, the NHC said.