South Bruce OPP are investigating a collision between a horse and buggy and a school bus in Arran-Elderslie.
Police say it happened at about 4 Thursday afternoon at Concession 10 Sideroad 5.
OPP, Saugeen Shores Police, Bruce County EMS and the Paisley Fire Department, responded.
The five people in the horse drawn buggy were all injured.
Two of them had life threatening injuries, one was airlifted.
The three others were transported to local hospital with unknown injuries.
OPP say there were students on the school bus at the time and no injuries have been reported.
The driver of the school bus was transported to hospital for medical assessment.
The road was closed for a number of hours but is now open.
The South Bruce OPP are asking anyone with information that can assist police to call 1-888-310-1122.
Should you wish to remain anonymous, call Crime Stoppers at 1-800-222-8477 (TIPS) or submit a secure web-tip at www.cstip.ca, where you may be eligible to receive a cash reward of up to $2,000.