Up to 1.5 million people were fleeing south Atlantic coastal areas as Hurricane Matthew regained strength as a Category 4 storm Thursday and eyed the United States.

The storm, which had dipped to a Category 3, roared back up Category 4 late Thursday morning, with maximum sustained winds at 140 mph, the National Hurricane Center said.

"Extremely dangerous Hurricane Matthew heading for Florida," the Hurricane Center warned in its 11 a.m. advisory.

Evacuations were under way in Florida, Georgia and South Carolina after Matthew, which hammered Haiti and strafed Cuba, began battering the Bahamas. The storm killed 25 people in the Caribbean, mostly in Haiti, and forecasters warned of "life-threatening" devastation as it crossed the Bahamas.

Latest developments:

Landfall or near-landfall is forecast for Thursday night, between West Palm Beach and Cape Canaveral, Florida.

Winds of 145 mph are expected at landfall, although there's a small chance the winds could reach Category 5 strength.

Regardless of whether Florida gets a direct hit from Matthew, historic damage will occur Friday along the state's east coast. Florida Gov. Rick Scott warned the impact would be "catastrophic."

Tropical storm conditions were expected in Florida Thursday before Matthew takes a turn to the north-northwest and approaches the east coast of the state's peninsula by Friday, the National Hurricane Center said.

Florida Gov. Rick Scott pleaded with residents to follow evacuation orders.

"Do not surf. Do not go on the beach. This will kill you," he said Thursday. "There is no reason not to leave."

Scott activated 2,500 members of the National Guard and warned Floridians that projected winds of 100 to 150 mph will destroy houses and "millions will lose power, possibly for a long period of time."

"My goal is to make sure everyone is prepared," he said, telling residents to fill up on gas and supplies now. "Evacuate, evacuate, evacuate."

The National Hurricane Center extended the hurricane warning Thursday northward to Altamaha Sound in Georgia, while a watch was put into effect as far north as South Carolina's South Santee River.

"Storm surges are going to go much further inland than people realize, and that's a lot of water all at once. The winds are going to be incredibly high, and the rain is what we're concerned about," South Carolina Gov. Nikki Haley said.

The projected path of the storm, according to the National Hurricane Center:

  • Thursday morning and afternoon: The worst conditions will occur in Nassau and New Providence in the Bahamas. Tropical storm conditions are first expected in Florida.
  • Thursday evening and Friday morning: A turn toward the north-northwest is expected as Matthew approaches Florida.
  • Friday afternoon and evening: Matthew will roll near the east coast of the Florida peninsula, with central coastal Florida experiencing hurricane conditions throughout the day.
  • Saturday morning: Depending on the position, coastal South Carolina or Savannah, Georgia, could have strong wind and rain.
  • Saturday afternoon and evening: Matthew could move eastward, with Myrtle Beach, South Carolina, feeling lesser impacts.