'Super fog' leaves seven dead in massive US highway pileup

This still image obtained from a handout video released by the Lousiana State Police on Facebook shows cars piled up after a crash on Interstate 55 highway in St. John the Baptist Parish, Louisiana, on October 23, 2023. Photo handout via AFP

The so-called "super fog," which US media reported was caused by a mixture of marsh fires and dense fog, led to a massive pileup on Interstate 55, about 30 miles (48 kilometers) outside of New Orleans, the Louisiana State Police said in a statement.

Photos posted by the police showed both lanes of the highway bridge where the incident occurred blocked off by the wreckage, which included dozens of charred vehicles.

A fire had erupted on the highway, police said.

One vehicle appeared to have driven off the bridge and into the water below.

More than 25 people were taken to hospital, not counting the "many victims (who) sought medical assistance on their own."

Super fogs form "when a mixture of smoke and moisture released from damp smoldering organic material such as brush, leaves and trees, mixes with cooler, nearly saturated air," according to the National Weather Service.

When they occur, visibility can drop to less than 10 feet (three meters).