Northbound lanes are now reopened.
Causeway General Manager Carlton Dufrenchou says officers are on the scene of a reported vehicle fire, and that a vehicle may have gone over the side into the lake.
A driver on the bridge describes the scene to WWL First News:
A vehicle "exploded" on the Southbound bridge and went overboard, according to Dufrenchou.
The Coast Guard is on the scene.
THIS IS A BREAKING NEWS STORY, please check back in a few minutes for an update.