A massive pileup is causing major traffic issues for travelers on Interstate 95 in South Carolina.

The collision occurred Thursday morning when dense fog was causing low visibility.

"Fog over Lake Marion formed near first light Thursday morning, then mixed out by around 10 a.m.," said Jonathan Belles, senior digital meteorologist for The Weather Company. "Visibility dropped below a quarter of a mile at times."

The pileup has prompted a long closure of the southbound lanes of I-95 on the bridge over Lake Marion, located about an hour east of Columbia.

Local news media outlets have reported estimates between 40 and 65 vehicles were involved. One reported that four people were trapped in their vehicles, and about 11 people were taken to the hospital with minor injuries.

Officials warned it would take “an extended period of time” to clear the bridge.

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“Just wanted to give you a firsthand look at what first responders are dealing with,” South Carolina Highway Patrol Trooper Nick Pye said in a video posted to social media. “We’re working with our tow truck partners in an effort to get these vehicles out of here. We gotta do it safely, we gotta make sure that we keep our first responders safe as well, but we’re working as hard as we can, doing everything we can, to make sure that we open this roadway up as soon as possible. Again, please avoid the area at all costs if you can."

Belles said that fog, like what led to this pileup, is more common in the fall as cooler air meets the summer's lingering humidity.

"It is most common in the morning hours when humidity is highest and then the fog mixes out as temperatures warm.," Belles said. "Fog is more common around bodies of water like lakes and rivers where humidity is locally highest."