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 storm was about 220 kilometres east-northwest of Cozumel, Mexico, with maximum sustained winds of winds of 120 kilometres per hour, forecasters said.
A hurricane warning was in effect for a more than 300-mile (480-km) stretch of coastline from the Florida-Alabama border to the Suwannee River in Florida. 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.
A hurricane warning was up across the Florida panhandle, a low-lying area of beachfront resort and retirement communities on north-eastern Gulf coast.
Bay County Sheriff Tommy Ford said he's "not seeing the level of traffic" he would expect when three-quarters of the county's residents are under mandatory and voluntary evacuation orders.
Forecasters said it could bring 3 to 6 inches of rain to Georgia, the Carolinas and Virginia, triggering flash flooding in a corner of the country still recovering from Florence.
While Florence wrung itself out for days and brought ruinous rains, fast-moving Michael is likely to be more about wind and storm surge.
Currently, the bulk of the forecast model guidance has the storm tracking southeast of the Maritimes, as well as Newfoundland this weekend. Most of that rainfall should hit Wednesday night and Thursday, and flooding could occur in the already saturated region, said meteorologist Andrew Kimball. The governor has also warned that there is a "significant" chance of tornadoes.
Officials in Bay County say they have not seen a rush of evacuees clogging roads inland - and that worries them with just hours left before Michael's landfall in the Panhandle.
"This storm will be life-threatening and extremely unsafe", Scott said at a news conference Sunday.More news: ‘Got another friend request from you’ scam hits Facebook
A search and rescue team from Tennessee has been deployed to Florida ahead of the expected arrival of Hurricane Michael. "Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other unsafe conditions", the hurricane center said.
Scott, after getting a briefing at 8 a.m.at the State Emergency Operations Center, urged people who plan to evacuate to do so Tuesday morning, as he continued to expand the activation of the Florida National Guard in advance of Michael's landfall.
"We are running out of time", the Republican governor said on Twitter.
He said, "There's nothing between us and this storm but warm water and I think that's what terrifies us about the potential impacts".
In the small Panhandle city of Apalachicola, Mayor Van Johnson Sr. said the 2,300 residents are frantically preparing for a major hurricane strike that could be unlike any there in decades.
The most recent October landfalling hurricane in the Florida Panhandle was Hurricane Opal - a Category 3 storm in 1995.
In Florida, state offices, schools and universities were set to close on Tuesday through the end of the week in panhandle counties.
Neighbouring counties within Tallahassee are covered by similar alerts, with hurricane and storm surge warnings in place across the entire state. Rainfall totals are expected to be between 3.5 and 4 inches.
The hurricane's effects will be felt far from its eye.
Images on social media showed evacuated families wading through water to get to safety.