(CNN) -- The southern East Coast of the United States is bracing for the arrival of Hurricane Florence as the storm -- already packing winds of up to 140 mph -- nears Category 5 strength.
More than 1 million people face mandatory evacuation orders in coastal areas of Virginia, North Carolina and South Carolina.
Tropical storm force winds are expected to reach the Carolina coasts late Wednesday night into early Thursday morning, CNN meteorologist Michael Guy said. Those states are also now under hurricane and storm surge watches.
"Hurricane wind gusts will likely begin being felt Thursday early evening as the storm begins to approach landfall," he said. "Inland areas of Raleigh, the Piedmont of North Carolina (Greensboro, Winston-Salem, High-Point), and Charlotte will likely see tropical storm force winds early Thursday afternoon as the hurricane continues to approach the Outer Banks along the coast."
Hurricane and storm surge watches were issued for portions of the coasts of the Carolinas Tuesday morning, the National Hurricane Center said.
The watches extend from Edisto Beach, South Carolina northward to the North Carolina-Virginia border, including the Pamlico and Albemarle Sounds. Those areas are at risk for hurricane conditions and "life-threatening inundation from rising water moving inland from the coastline" during the next 48 hours, the NHC said.
Storm is expected to strengthen
As of 5 a.m. ET Tuesday, Florence had maximum sustained winds of 140 mph, the National Hurricane Center said. The storm is expected to pick up speed, strengthening to near Category 5 strength within the next 24 to 36 hours, the center said. It is expected to be an "extremely dangerous major hurricane" through Thursday night, the NHC said. A Category 5 storm has sustained winds of 157 mph or more.
Florence has quickly intensified since forming. The storm became a hurricane on Sunday. By Monday morning, it had grown to a Category 3 storm. About an hour after the Category 3 upgrade, it was reclassified as Category 4.
Florence has been gaining strength from the Atlantic's warm waters over the past 24 hours. It is likely to bring a number of hazards when it reaches land including dangerous storm surge and lingering rain, which could produce flash flooding, the National Hurricane Center said.
"The areas along the coast are likely to see the biggest impacts as far as damage from storm surge and wind at landfall -- then as the storm system lingers through the weekend there will be heavy rain and flooding throughout the Mid-Atlantic region with the biggest flood threat in the Carolinas," Guy said.
States of emergency declared in four states
One year after major storms ravaged the Gulf Coast and Puerto Rico, officials warned those in Florence's path not to underestimate the threat the storm poses.
States of emergency were declared in the Carolinas, Virginia and Maryland. In Maryland, where some coastal areas are still recovering from weather, Gov. Larry Hogan said flooding could be catastrophic if it hits the state.
"We are hoping for the best and preparing for the worst," Hogan said.
North Carolina Gov. Roy Cooper urged residents to prepare for lengthy power outages after the hurricane arrives and learn evacuation routes they may need to take. Six more North Carolina counties were placed under mandatory evacuation Monday night, hours after the first order in Hatteras Island. Certain areas of Brunswick, Currituck, Dare, Hyde, New Hanover, and Onslow counties are affected, and more orders are expected Tuesday.
"North Carolina is taking Hurricane Florence seriously, and you should, too," Cooper said. "Action today can avoid losses due to Florence."
In South Carolina, mandatory evacuation orders take effect Tuesday at noon in eight counties along the state's 187-mile coastline. Starting then, all roads on I-26 and Route 501 will be directed away from the coast, South Carolina Gov. Henry McMaster said.
State government offices, including schools and medical facilities, will be closed in 26 counties, McMaster said. He estimated that about 1 million people will be affected by the order, including residents and visitors.
"This is a real hurricane we have coming," McMaster said Monday. "We don't want to risk one South Carolina life."
In Virginia, mandatory evacuations begin at 8 a.m. Tuesday for about 245,000 residents in a portion of Hampton Roads and the Eastern Shore area, Gov. Ralph Northam said Monday.
"Everyone in Virginia needs to prepare," he said. "This is a serious storm and it's going to affect the entire state of Virginia."
National Guard soldiers are being mobilized in the affected states. President Donald Trump declared an emergency in North Carolina, allowing it to access federal funds.
Residents prepare to flee and hunker down
Residents along the coast boarded up their homes, formed long lines at gas stations and emptied the shelves of hardware stores and supermarkets Monday as they prepared for Florence's arrival.
Crystal Kirwan didn't think she had much choice as she got her family ready to leave their home in Moyock, North Carolina, Monday. She and her husband will make the 4.5-hour drive with their children to family in Dover, Delaware, as soon as he is cleared from military duty.
"Probably not too much better, but most likely safer than here," she said.
Grocery stores began selling out of water, milk and bread, and supply stores were struggling to stock batteries, plywood and generators as early as Sunday.
At a Home Depot in Wilmington, North Carolina, Billy Nivens told CNN they ran out of water, plywood, generators, flashlights, propane, batteries and five-gallon gas cans by Monday afternoon.
Ryan Fonville visited three hardware stores in Wilmington Monday and found that they were running out of supplies.
"I gathered my supplies this weekend, sharing for local community groups so people don't waste gas. The gas pumps are running out as well," Fonville told CNN.
Since noon Sunday, a Lowe's in Lumberton, North Carolina has been sold out of generators, store manager Mackie Singletary said.
In Charleston, South Carolina, the Coburg Dairy Cow landmark was removed for safekeeping from its perch atop a sign on Highway 17 on Monday, according to CNN affiliate WCIV.