The death toll in the Bahamas from Hurricane Dorian rose sharply Wednesday as the storm strengthened slightly and headed toward the Carolinas, where some of the worst flooding in 30 years was expected beginning Thursday.

Bahamas Health Minister Duane Sands told NBC News on Wednesday that 20 deaths had been confirmed so far and that the number was expected to rise. Prime Minister Hubert Minnis had called Dorian "one of the greatest national crises in our country's history" on Tuesday, when only seven deaths had been confirmed.

Sands said Wednesday: "We've had an absolute horrendous tragedy, numbers of lives lost, and we have not completed the door-to-door."

Minnis scheduled a nationwide address for Wednesday night.

President Donald Trump said the U.S. Coast Guard was headed for the Bahamas to provide humanitarian relief.

North Carolina Gov. Roy Cooper pointed to the devastation in the Bahamas to urge people to take evacuation orders seriously. He activated 300 National Guard members and issued evacuation orders for all barrier islands beginning Wednesday.

"We have seen the life-and-death effects of this storm in the Bahamas, and we urge everyone on the islands at the coast to leave," Cooper said in a statement.

The National Hurricane Center said Wednesday night that Dorian had strengthened slightly, with maximum sustained winds of 110 mph, as it tracked north-northwest at 8 mph about 130 miles south of Charleston, South Carolina.

The Latest on Dorian:

  • The hurricane was about 130 miles south of Charleston, South Carolina, Wednesday evening and was moving north-northwest at 8 mph.
  • The storm had maximum sustained winds of about 110 mph.
  • At least 20 people have died in the Bahamas, and more deaths are expected to be reported, the prime minister said.
  • Officials said Dorian was set to move near or over the South Carolina coast on Thursday and then near or over the North Carolina coast on Thursday night and Friday.

The hurricane center said Dorian would approach the South Carolina coast Wednesday night and move near or over the coast Thursday. It was expected to move near or over the North Carolina coast on Thursday night and Friday.

A hurricane warning was in effect for north of Savannah River, which divides South Carolina and Georgia, to the North Carolina-Virginia border, including Pamlico and Albemarle sounds. Tropical storm warnings and watches extended as far north as Fenwick Island, Delaware.

"Life-threatening storm surge with significant coastal flooding is expected along a large portion of the Southeast and Mid-Atlantic coasts of the United States during the next couple of days," the hurricane center said.

South Carolina appeared to be in line for some of the worst.

High tides were expected to top 9½ feet on Wednesday afternoon and then 10½ feet early Thursday along Charleston Harbor, the National Weather Service said. Flooding occurs when tides reach 7 feet.

"Time to get out is running out," South Carolina Gov. Henry McMaster warned Wednesday. "Once the wind speeds get up to about 40 or 45 miles an hour, emergency crews will not be able to come in and get you."

Since Monday afternoon, 100 miles of Interstate 26, from coastal Charleston to inland Columbia had been running one way, west. Lane reversals were being returned to normal on Wednesday, the state Public Safety Department said, but Charleston Mayor John Tecklenburg said he wanted his city empty and shuttered.

"Starting late this afternoon, for 36 hours, I want Charleston to be a ghost town," he said at a news conference Wednesday. "I want everybody out of sight ... inside, hunkered down and safe."

Federal emergency declarations have been approved for four states — FloridaGeorgiaSouth Carolina and North Carolina — and the governor of Virginia has also declared a state of emergency.

While there had been no recorded deaths as a result of storm conditions in the United States, at least two people have died while making preparations in the last few days.

A 55-year-old man died Monday after falling about 15 feet from a treein Ocoee, Florida, the fire brigade said. The man, who wasn't named, was pronounced dead at a hospital.

"He was in a tree cutting limbs in preparation, and then a limb broke lose," said Corey Bowles of the Ocoee Fire Department. "He was preparing for the storm."

On Sunday, David Allen Bradley, 68, of Indialantic, Florida, died after falling from a ladder on his third-story balcony, police said. He was putting plywood on his windows, Police Chief Michael Connor said in an email early Wednesday.

Separately, a 61-year-old man died while swimming in the Atlantic Ocean near Hatteras Village, North Carolina, on Sunday, the National Park Service said.

The park service said the cause of death was unknown but that a high risk of rip currents had been forecast for most of the beaches along Hatteras National Seashore on Sunday. It was unclear whether the man was caught up in a rip current.

In Florida, things could have been much worse.

Video showed winds and rain hitting parts of St. Augustine Beach, the coast southeast of Jacksonville, Cocoa Beach and other areas, but state officials said there had been no reports of major damage as Dorian passed near Daytona Beach.

Volusia County emergency management officials tweeted Wednesday that all bridges were closed to eastbound traffic. The sheriff's office said it was prepared with high-water rescue teams if needed.