Gaston made landfall near McClellanville, a small fishing village that was brushed by Hurricane Charley earlier this month when it came ashore for a second time after devastating southwest Florida.
Gov. Mark Sanford declared a state of emergency Sunday and encouraged residents to stay in their homes so damage-assessment crews and utility and cleanup workers could do their work.
As much as 10 inches of rain fell in Charleston County, and a flash flood watch was in effect along some parts of the coast. Hundreds of residents were urged to evacuate ahead of the storm.
Hours after the eye of Gaston came ashore, steady sheets of rain drenched Mount Pleasant. Tree limbs littered flooded roadways, some of which were impassable. Palmettos were pushed to the pavement, and road signs twisted in the wind.
Across the harbor in Charleston, Gaston flooded streets and toppled power poles. At least 125,000 people were without power at the height of the storm.
The rain tapered off along the coast by midday, but blustery wind still raked the coastline near Charleston, and intersections throughout the area had no traffic lights.
"The important thing is that we don't have any false sense of safety that it's all over," said Charleston Mayor Joseph P. Riley Jr. "We have downed trees, and often times there are power lines under those downed trees."
By evening, Gaston was moving north about 8 mph across inland South Carolina, weakening along the way but still packing wind gusts as high as 82 mph.
Charleston County officials said there was only one initial report of a serious injury — a resident injured when a tree fell on a home.
"It just goes to show that the residents took the proper precautions that they needed to take and shows they were prepared," said Roland Windham, the Charleston County administrator.
Residents in low-lying areas in Charleston and Georgetown counties were urged to move to higher ground before the storm hit. Authorities also asked people living in mobile homes to evacuate.
"We hope we don't experience any more injuries during the cleanup," Windham said. "That's typically when you see a lot of injuries occur."
John Legare of the state Emergency Management agency said about 30 people had sought refuge in five shelters in coastal counties as Gaston approached. Shelters were opened in at least one inland county.
Gaston had maximum sustained winds of 70 mph when it hit land but was down to 45 mph by early afternoon. Forecasters said the weakened storm could reach North Carolina by Sunday night.
By mid-afternoon, bands of rain had reached North Carolina. No flooding was reported, but strong winds tore the roof from a house in Laurinburg, officials said.
In South Carolina, Legare said, the storm had picked up speed, which could mean less flooding.
"The faster it moves, the less chance it has to rain," Legare said. "But until it has passed through, I don't think we can say flooding is not a concern."
In Charleston, water stood in the street in front of the palatial homes on the city's waterfront. Debbie Rice-Marko was cleaning tree limbs and other debris from the front of her 250-year-old house, which was left with knee-deep water in the basement.
"We didn't see anything like this with Charley," she said, noting residents have had to deal with Bonnie, Charley and Gaston already this year. And they are now eyeing Hurricane Frances spinning in the Atlantic Ocean.
Frances had sustained winds of 135 mph about 495 miles east of the Leeward Islands in the southeastern Caribbean. Hugh Cobb, a meteorologist at the National Hurricane Center in Miami, said the storm was traveling over warm water, which is a favorable condition for intensification.
The National Hurricane Center in Miami said people from Cuba to the southeastern United States should closely monitor the progress of the storm, which could strengthen on Sunday and threaten land by Labor Day weekend.
Meanwhile, Tropical Storm Hermine formed in the Atlantic, the eighth named storm of the season. The center of Hermine was about 325 miles southeast of Cape Hatteras, N.C. The storm was moving toward the northwest near 10 mph and maximum sustained winds were near 40 mph.