TALLAHASSEE, Fla. - Powerful Hurricane Michael closed in on Florida's northwestern shore on Wednesday with the threat of catastrophic surges of sea 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 am ET (1200 GMT) was carrying top winds of 145 miles per hour (230 km per hour), the National Hurricane Center said

It 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.

Michael's menace was compounded by its relatively quick development, growing from a tropical storm to Category 4 hurricane in about 40 hours.

More than 2.1 million residents of at least 20 Florida counties were under mandatory or voluntary evacuation orders.

Much of the area is rural and known for small tourist cities, beaches and wildlife reserves, as well as Tallahassee.

"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. US 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.

Reuters