A crash involving an ambulance carrying a patient and a car sent four people to hospital Tuesday night.

South Simcoe Police say the head-on collision happened at about 9:45 p.m. near Innisfil south of Barrie

The ambulance was responding to a call with lights and siren activated at the time of the crash.

The driver of the car suffered serious injuries while two paramedics and a student aboard the ambulance were also taken to hospital for treatment.

The extent of their injuries was not revealed, although police say the paramedics were able to tend to the injured driver before other crews arrived to take over.

Weather and speed are being considered as factors in the collision.