The storm was about 220 kilometres east-northwest of Cozumel, Mexico, with maximum sustained winds of winds of 120 kilometres per hour, forecasters said. The hurricane is expected to make landfall in Florida's Panhandle or Big Bend on Wednesday before crossing Georgia and the Carolinas as a weaker storm.
He added that it is predicted to be "the most destructive storm to hit the Florida panhandle in decades". "The time to prepare is now".
Energy companies halted almost a fifth of Gulf of Mexico oil production and moved staff from 10 platforms on Monday as Michael was forecast to become the strongest of three named storms to affect the US Gulf of Mexico this year.
The Gulf of Mexico produces 17 percent of daily U.S. crude oil output and 5 percent of daily natural gas output, according to the U.S. Energy Information Administration. The partial shutdown ahead of Michael helped drive oil prices slightly higher on Tuesday.
He said tolls were being suspended in the state's northwest region to ease the evacuation process, and the Florida Highway Patrol is sending almost 350 state troopers to the Panhandle and Big Bend areas.
Florida governor Rick Scott has declared a state of emergency in 35 counties, warning that the region must be "prepared for a direct hit with sustained hurricane force winds". "You will see power outages", said Jeff Byard, associate administrator for the Federal Emergency Management Agency's Office of Response and Recovery. About 1,250 National Guard soldiers were assisting and more than 4,000 troops were on standby. As much as a foot (30 cm) of rain is forecast across Florida, Georgia and SC, the center reported.
State offices, schools and universities were to close on Tuesday through the end of the week in panhandle counties. Lines at gasoline stations grew as people left.
"It looks like what we are planning for Wednesday is tropical storm-force winds of 39 to 57 miles per hour", said Jonathan Lord, Flagler County's emergency services chief. Because he owns two businesses in the area, Givens, who lives inland, said he was not evacuating.
The only other storm in the Atlantic Ocean is Tropical Storm Leslie, which has zig-zagged in intensity.
Late Monday, residents of far western Cuba were forecast to get up to eight inches of rain.
Interaction between Michael and a high pressure system to the north were creating windy and hazardous conditions along local beaches Monday, coinciding with seasonal high tides. "It's forecast to be a large and risky hurricane at landfall". The center of Michael is expected to move inland over the Florida Panhandle or Florida Big Bend area on Wednesday.
More than 45 per cent of the nation's refining capacity is located along the US Gulf Coast, which also is home to 51 per cent of total US natural gas processing capability.
Georgia Governor Nathan Deal declared a state of emergency on Tuesday for 92 counties in his state. By comparison, Florence caused upwards of 20-30 inches of rain across much of the Carolinas.