Police are investigating what caused four freight train cars to derail at a busy intersection near Barrio Logan Wednesday evening, on the San Diego side of the Coronado Bridge.

The incident was reported just after 8 p.m. at the intersection of East Cesar Chavez Parkway and Harbor Drive. It is unclear what caused the Burlington Northern Santa Fe train to derail.

Police say the cars were carrying vehicles inside. No injuries were reported.

Early Thursday morning, crews were working to right the trains. A BNSF spokesperson said they were using what is known as a side broom to tilt the cars so that workers could get the wheels put back on them. They would then be lifted back on the tracks and realigned.  

BNSF was hoping to have the tracks cleared by noon. Meanwhile, a Sig Alert was in effect for Cesar Chavez Parkway, which was closed at Harbor Drive.

The track is mainly used to export vehicles and petroleum, the spokesperson said.

The cause of the derailment is under investigation.