Chatham-Kent police officers are asking for help finding a potential witness to a serious crash between a minivan and an ambulance earlier this week.

Police believe the driver of a commercial vehicle might have seen the crash on Queens Line on near Highway 401 Wednesday morning. It passed the ambulance travelling in the opposite direction before the collision.

Immediately after the crash, police say the driver of the commercial vehicle stopped, then drove away. It is not alleged this driver had anything to do with the collision.

Investigators have spoken with multiple other people that witnessed the crash.

Both drivers in the crash were sent to hospital with serious injuries, say police. The driver of the minivan remains in critical but stable condition. The driver of the ambulance remains in stable condition.

The traffic unit is asking the commercial driver to contact police. Any member of the public who knows the identity of the driver is also asked to call police. Callers may contact Const. Michael Pearce at 519-355-1092 or Crime Stoppers at 1-800-222-TIPS (8477).