South Carolina Governor Nikki Haley -- calling the torrential downpours "unbelievable" -- told reporters that 14 people had died due to the severe weather in her hard-hit state, up from a previous toll of 11.
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 in the midst of a storm.
Haley, who on Sunday called the extreme floods a once-in-a-thousand-year event -- 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."
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The National Guard and the Department of Transportation were on standby, she added.
In other comments, Haley said 40 percent of first responder calls in her state were linked to road accidents, urging the population 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.