Seven people have been killed and dozens more injured after a “super fog” descended on a Louisiana highway, causing a 158-car pileup.
The fog, which is created when smoke from smouldering undergrowth mixes with cooler air and water vapour, covered Interstate 55 near New Orleans on Monday morning, reducing visibility to near zero.
State police said a major crash of more than 158 vehicles had caused a portion of the road to catch fire and totaled a tanker truck carrying “hazardous liquid”.
Seven deaths have been confirmed but police said more casualties may be discovered as emergency services comb through the wreckage. More than 25 people have been taken to hospital.
The crash took place in St John the Baptist Parish, northwest of New Orleans, on an interstate next to Lake Pontchartrain, the second largest inland saltwater body in the United States.
The road runs through a swap where smouldering material is understood to have produced smoke and water vapour, which mixed with colder air to create the “super fog”.
More than four fifths of Louisiana is currently experiencing extreme drought, which has caused dry marshland to catch fire.
According to the US National Weather Service (NWS), the smoke can be produced from “organic material such as brush, leaves and trees”, and reduces visibility to less than ten feet (three metres) when it becomes fog.
“Under light wind conditions, super fog meanders through low terrain areas such as creek beds or drainage ditches,” the NWS said.
“Super fog can be very dangerous when present over highways, and has been the cause of several large, multi-vehicle pileups.”
The service released a dense fog warning for much of southeast Louisiana, including the area between Baton Rouge and New Orleans where the crash took place.
A police spokesman said that first responders “continue to search for victims of the crash”.
“Preliminary investigation revealed that at least 158 vehicles were involved in this morning’s crash,” the spokesman said.
“That total is from both north and southbound lanes. Seven fatalities have been confirmed.
“Over 25 individuals were transported to area hospitals with varying degrees of injuries from critical to minor. Many victims sought medical assistance on their own.”
“It is possible that additional fatalities could be located.”
John Bel Edwards, the Louisiana governor, said: “The combination of wildfire smoke and dense fog is dangerous, and I want to encourage all Louisianans in affected areas to take extreme caution when travelling.”