Durham Regional Police tweeted shortly before noon that they were responding to a serious two-vehicle collision in the area of County Road 23 and Thorah Concession 4 Road.
Police later confirmed that a woman and two men in a vehicle were killed in the crash.
Another woman and a child in a second vehicle were seriously injured, police said.
The cause of the collision is unknown.
@DRPSNorthDiv members are on the scene of a serious collision at Reg Rd 23 and Thorah Concession Rd in Brock Township. More information will follow as it becomes available. Avoid this area. pic.twitter.com/jWHJqqhbpn
— Durham Regional Police (@DRPS) July 1, 2022