Mike Conroy of the Virginia State Police said the massive accident began about 1 p.m.
"Fog was a major contributing factor. I am assuming it was one accident and then a cluster after that," Conroy told The Carroll News.
The smashed vehicles were strewn over a stretch of one-half to three-quarters of a mile, forcing the closure of the interstate's southbound lanes for about 30 miles from Fort Chiswell to Lambsburg so emergency vehicles could get to the victims.
"It's the worst accident I've ever seen," Virginia State Police 1st Sgt. Mike Musser told the newspaper.
Lee Lewis of Charleston, W.Va., who was on his way to Hilton Head Island, S.C., with his family, said motorists had ignored a posted message to slow down for dense fog.
"It was way too foggy and cars were going way too fast. I was going 40 to 45 miles per hour," Lewis said. "You couldn't see but about 30 feet in front of you. A car in front of us stopped and it piled up from there. I rolled my window down and you could just hear car after car crashing behind us. My family was able to get up to a bank untouched."
Joan Jenkins of Canada said she and her husband were unscathed despite their car being smacked twice by tractor-trailer rigs, the New said.
"We feel very lucky," Jenkins said. "After we got hit, we got out and my husband started screaming for us to run. Our thought was just to get out of there. We heard the cars crashing behind us. Another truck came and ran over top of our car. We were so thankful we weren't hurt. We were just happy we were able to send messages to our children and say we were OK. It was unbelievable."
2014: The Year in Music [PHOTOS]