© National Weather Service Charleston, S.C./Twitter Flash floods caused by torrential 'once-in-a thousand-year' rainfall in South Carolina.
The storm had dumped more than 45 centimetres of rain in parts of central South Carolina by early Sunday.
The state climatologist forecast another 5 to 15 centimetres through Monday as the rainfall began to slacken.
"We haven't seen this level of rain in the low country in 1,000 years," South Carolina governor Nikki Haley told a news conference.
"This is not something to be out taking pictures of. This is not something that you want your kids playing in. The water is not safe.
"And a lot of areas across the state where you see this deep water, it's got bacteria in it. So stay inside and don't get in there.
"This is an incident we've never had before."
Six weather-related deaths were reported in South Carolina, four of them from traffic accidents. Officials reported another two deaths in North Carolina.
President Barack Obama declared a state of emergency in South Carolina on Saturday, ordering federal aid for areas affected by flooding.
Precipitation records fell in many places. In less than four days, Charleston broke its record for the greatest monthly rainfall for October.
Counties reported more than 200 rescues from flood waters since Saturday night and more are expected, the emergency management division said in a Twitter post.
The storms are part of a separate weather system from Hurricane Joaquin, which was downgraded on Sunday to a Category Two storm as it headed towards Bermuda.
Flooding causes major road closures
Overnight rains flooded highways along the South Carolina coast between Charleston and Georgetown, the National Weather Service said.
Georgetown, population 9,000, was mostly under water, and the four major highways leading into it were closed.
"We have every ambulance in the county out responding to calls. People are being moved from their homes in boats," Georgetown County spokeswoman Jackie Broach said.
Inland flooding also hit South Carolina's capital, Columbia, where the Congaree River rose 3 metres in 12 hours, according to local officials.
Columbia posted a record 22 centimetres of rain in 24 hours ending Sunday afternoon, the weather service said.
A 112-kilometre stretch of Interstate 95, a major East Coast highway, was closed because of high water.
State emergency officials urged residents not to travel due to unsafe roads, and curfews were imposed in several places, including Columbia.
Schools and universities cancelled classes on Monday.
Source: Reuters/AFP
Comment: All over the world torrential rainfall is breaking records and causing 'historic' flooding and devastating mudslides. In the past two weeks alone some incidents include: