California Highway Patrol is investigating a crash that left six people dead in the Northern Sacramento Valley on Wednesday.

Officers say, around 10 a.m., a Tehama County transit bus (TRAX) was struck head-on by a pickup truck along Highway 99W near Gyle Road near the community of Corning.

The pickup truck had crossed over into the opposite direction of traffic, officers say.

Five people, plus the driver, were on board the TRAX bus – which was soon engulfed in flames after the crash. Four people from the bus, along with the driver, died at the scene, CHP says.

The pickup driver also died at the scene, officers say. No one else was riding in the pickup.

Exactly what led up to the crash is still under investigation. CHP says they don't know, at this time, if drugs or alcohol were factors.

Due to the crash, TRAX has suspended all transit service on Wednesday.

"Our thoughts are with those impacted during this difficult time. Transit service will resume when the program is operationally able to do so," Tehama County Public Works said in a statement.

No information about any of the people who died has been released yet.

The area where the crash happened is about 40 minutes south of Redding and two hours north of Sacramento.