CHARLESTON, S.C. - Torrential rainfall that South Carolina's governor called a once-in-a-millennium downpour triggered flooding in the southeastern US state on Sunday, causing at least eight deaths in the Carolinas.The storm had dumped more than 18 inches (45 cm) of rain in parts of central South Carolina by early Sunday. The state climatologist forecast another 2 to 6 inches (5 to 15 cm) through Monday as the rain began to slacken.South Carolina Governor Nikki Haley said parts of the state were hit with rainfall that would be expected to occur once in 1,000 years, with the Congaree River running at its highest level since 1936."If you are in your house, stay in your house," Haley, holding a news conference, told state residents. "This is not something to be out taking pictures of."Six weather-related deaths were reported in South Carolina, four of them from traffic accidents. Officials reported another two deaths in North Carolina.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.