As Hurricane Florence barrels toward the Southeast as a Category 4 storm, South Carolina’s governor has ordered evacuations along the state's entire coastline — which could affect up to a million people.

“We know that this evacuation order is going to be inconvenient for some people,” Gov. Henry McMaster, R-S.C., said in a press conference on Monday afternoon, “but we do not want to risk one South Carolinian’s life.”

Schools will be closed starting Tuesday in the affected counties and state officials will reverse lanes on four major roads leading to the coast to assist with the evacuation.

“We are not going to gamble with the lives of the people of South Carolina,” McMaster said.

North and South Carolina are anticipated to bear the brunt of Florence, which the National Hurricane Center said on Monday had strengthened to a Category 3 storm. An hour later, at noon, the agency tweeted that Florence had grown again to a Category 4, with maximum sustained winds near 130 mph.

In North Carolina, evacuations were already underway: Dare County officials issued a mandatory evacuation on Monday for Hatteras Island in the Outer Banks, and ordered more evacuations for other areas of the county beginning Tuesday morning.

While the storm could weaken some before making landfall, forecasters expect it could still be a Category 3 or 4.

Gov. Roy Cooper, D-N.C., warned residents to take the threat of the storm seriously.

"The forecast places North Carolina in the bull's-eye of Hurricane Florence, and the storm is rapidly getting stronger," he said. "When weather forecasters tell us 'life-threatening,' we know that it is serious."

North Carolina should brace for three dangers from Florence, Cooper said: coastal ocean surges, strong winds and flooding.

"All parts of the state could be affected by the storm," Cooper said at a press conference on Monday morning, warning that power outages could last for "awhile."

Florence is currently 575 miles south-southeast of Bermuda and about 1,230 miles east-southeast of Cape Fear, North Carolina, moving west at 13 mph.

Cooper, who declared a state of emergency for North Carolina over the weekend, has already activated 200 National Guard troops, and asked President Donald Trump for a disaster declaration ahead of the storm so federal help can be made available as quickly as possible.

The governors of South Carolina and Virginia also declared states of emergency in advance.

On Sunday, South Carolina's state emergency management agency tweeted it was "preparing for the possibility of a large-scale disaster."

The hurricane is expected to approach the coast of South Carolina or North Carolina on Thursday, according to the National Hurricane Center.

But those in its path weren't wasting time. Shelves in some grocery stores in Raleigh, North Carolina, were already bare, and residents were filling up their gas tanks, reported NBC affiliate WRAL in Raleigh.

"Just in case I might have to make a quick getaway, I have a full tank of gas and I'm ready," Raleigh resident Tony Johnson told WRAL.

In Lexington County, South Carolina, officials asked homeowners with ponds with dams on their property to lower water levels ahead of landfall to try to avoid dams from overflowing, reported NBC affiliate WISC in Columbia, South Carolina.

Meanwhile, in Virginia, Dominion Energy utility crews were securing power lines ahead of the hurricane in anticipation of downed trees, according to NBC 12 in Richmond, Virginia.

A Trump campaign rally scheduled for Friday in Jackson, Miss., was canceled due to the storm.