VIDEO - 7 dead in crashes involving 150 vehicles on Louisiana interstate

"Once the tanker is removed, first responders will be able to better assess the vehicles in that immediate area. It is possible that additional fatalities could be located," police said.

At a news conference Monday, State Police Sgt. Kate Stegall said the crashes began shortly before 9 a.m. and stretched across a mile.

Stegall said that the investigation was fluid and that said the interstate will remained closed throughout the night Monday while the wreckage is cleared.

State police cautioned drivers about fog in a Facebook post about the crashed Monday morning.

"There is heavy fog in the area and drivers should avoid the area if possible and use alternate routes," the post said.

Video of the aftermath of the pileup shows foggy conditions and at least one instance of pickup on top of another vehicle.

There were multiple fires, including marsh fires, in the area, the National Weather Service in New Orleans said Monday on X.

Dense fog and smoke combined to form "Superfog," which was "heavily impacting" parts of the interstate, the weather service said.

State police told reporters around midday that one vehicle went over the highway guardrail and into the water but that the driver escaped unharmed. The interstate passes over swamp and open waters between Lake Maurepas and Lake Pontchartrain.

Gov. John Bel Edwards asked for prayers for those killed and injured in a statement on X. He also pleaded for people to donate blood.

"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 traveling," he said. "I also want to thank first responders and medical personnel who have worked so diligently to save lives and render aid."

Antonio Planas is a breaking news reporter for NBC News Digital. 

Assignment editor

Maya Brown and The Associated Press contributed.