NASSAU, Bahamas — Hurricane Dorian left stretches of the Bahamas looking as if they had been carpet bombed, and was regaining strength as it crawled up the US Atlantic coast, possibly making landfall later on Thursday in South Carolina.

The United Nations said 70,000 people in the Bahamas needed immediate humanitarian relief after the most damaging storm ever to hit the island nation.

Aerial video of the worst-hit Abaco Islands in northern Bahamas showed widespread devastation, with the harbor, shops, workplaces, a hospital, and airport landing strips damaged or blown to pieces, all of which was frustrating rescue efforts.

One of the most powerful Caribbean storms on record, the Category 5 hurricane killed at least 20 people in the Bahamas. Authorities expected that number to rise, Prime Minister Hubert Minnis told a news conference, as retreating floodwaters reveal the scope of destruction.

With many telephones down, residents posted lists of missing loved ones on social media. One Facebook post by media outlet Our News Bahamas had 2,000 comments, mainly listing lost family.

Dorian killed one person in Puerto Rico before hovering over the Bahamas for two days with torrential rains and fierce winds that whipped up 12-18 foot (3.7- to 5.5-meter) storm surges.

In the United States, South Carolina was preparing for a record storm surge, potentially reaching a height of 8 feet (2 meters) at the popular vacation destination of Myrtle Beach, the US National Hurricane Center (NHC) said in an advisory.

About a foot of rain will drop on flood-prone Charleston, South Carolina and many parts of the coasts of the Carolinas on Thursday and Friday, said Bob Oravec, a forecaster with the National Weather Service's Weather Prediction Center in College Park, Maryland.

"It's pretty substantial," he said. "It's already raining heavy in Charleston and up and down the coast," he said early Thursday.

Media reported flooding in historic downtown Charleston before sunup early Thursday, and more than 76,000 homes and businesses were without power along the state's coastal areas, according to the tracking site poweroutage.us.

Dorian is predicted to move near or over the coast of South Carolina later Thursday and then North Carolina overnight, forecasters said.

At 5 a.m. EST on Thursday, Dorian was about 80 miles (130 km) south-southeast of Charleston, the NHC said.

It had strengthened to regain its status as a Category 3 storm late on Wednesday with winds of 115 mph (185 kph), after passing over warm waters which drive hurricane intensity, the NHC said.

The NHC issued a storm surge warning that covered the parts of the coasts of Georgia, South Carolina and North Carolina stretching from the Savannah River and extending to southern Virginia.

More than 2.2 million people in Florida, Georgia, North Carolina and South Carolina have been ordered to evacuate, although Florida has avoided a direct hit.

An international relief effort was underway for the Bahamas, with a British Royal Navy vessel providing assistance and Jamaica sending a 150-member military contingent to help secure Abaco and Grand Bahama, officials said.

Volunteers also ferried supplies to the islands in a flotilla of small boats.

"Let us give of our best in this moment of historic tragedy," Minnis said.

He also encouraged international tourists to visit the Bahamas, which relies heavily on its hospitality industry.

As many as 13,000 homes in the Bahamas may have been destroyed or severely damaged, the International Federation of Red Cross and Red Crescent Societies said.

The State Department said it did not believe any US citizens in the Bahamas during the storm were killed.

President Donald Trump said the United States was sending supplies, including materials originally intended for any Dorian victims in Florida. — Reuters