Update, 9:25 a.m. Thursday:
All southbound lanes on the Lake Pontchartrain Cause Bridge are now open.
An accident on the Lake Pontchartrain Causeway Bridge has shut down southbound traffic Thursday morning.
Alternate routes are I-55 southbound or I-10 westbound.
State officials announced the closure of the southbound lanes around 7:10 a.m. It wasn't immediately clear when the lanes would reopen.