Large swathes of South Carolina remained under water and under threat from failing dams Wednesday, as the death toll from record floods in the southeastern United States rose to 17.

In South Carolina, 15 people have been confirmed dead in accidents related to the flooding, Crystal Buchanan of the state's Emergency Management Division told AFP.

Nine people were drowned and six were in traffic accidents, she said.

In neighboring North Carolina, first responders said two people lost their lives. One died when a tree toppled onto a car, and another in an accident that occurred mid-storm.

On Wednesday morning, officials urged residents of some 900 homes near South Carolina's Beaver Dam to immediately move to higher ground.

Even though rain has tapered off, rivers continue to overflow and 11 dams have failed since heavy rain began pounding the state on October 1.

An additional 35 other dams are being monitored, Buchanan said.

Meanwhile, some 75 miles (120 kilometers) of Interstate 95, a main north-south artery, are closed due to flooding, Buchanan said.

"Water continues to rise and crest," she said. "We're still responding to this historic rainfall."

A tropical air mass over much of South Carolina caused the sudden and dramatic flooding, burst dams, downed power lines and left residents scrambling for safety.

On Tuesday South Carolina Governor Nikki Haley said multiple dams had failed but that authorities were doing everything possible to monitor them and take necessary action.

"It is all hands on deck, it really is, everybody is doing whatever it takes," Haley said. "We're putting eyes on these dams, we're not just looking and saying what could happen."

The National Guard and the Department of Transportation were on standby, she added.

"We have vulnerable ones that we'll be watching today and through the next 36 hours," Haley said.

The governor also urged people to heed barriers that had been put up at some 500 submerged streets and bridges.

More than 800 people are still seeking refuge in 26 emergency shelters and numbers could still go up, she said.

Haley appealed to the population to stay strong and to follow instructions from authorities.

"Everything is moving as it should and I hope that gives people strength to know that we've got you," she said.

"The damage is going to be heartbreaking for a lot of people but it's not something that we can't go and rebuild, and refix and redo and that's the part that we have to focus on."

President Barack Obama signed a disaster declaration on Monday, making federal aid available to the state.