The crash occurred on I-55 in St. John the Baptist Parish, just outside of New Orleans,
More than 25 people were taken to hospitals with injuries ranging from critical to minor, police said. An unspecified number of people also went to medical facilities on their own, police said. One vehicle went off the interstate and into the water, but the driver was safely rescued, police said.
"A portion of the crash scene caught on fire shortly after the initial incident. One tanker truck carrying a hazardous liquid is being off-loaded due to a compromised tank/trailer," Lt. Melissa Matey of the Louisiana State Police said in a statement.
Matey said search crews may find more fatalities once the tanker is removed and they are able to access the vehicles near it.
Video from the scene posted on social media showed dense fog and dozens of damaged vehicles.
The low visibility was attributed to a so-called "super fog," a mixture of wildfire smoke and fog with visibility only as high as 10 feet, CBS affiliate WWL-TV reported.
Police said I-55 will remain closed until at least midday Tuesday, according to WWL-TV.
RHM/PR