A police officer and the suspect he was chasing have prompted a massive search effort after both fell into a gorge on the Canadian side of Niagara Falls during the pursuit.
The two men fell into the 30m-deep gorge about 9.30am NZST this morning after the suspect jumped a retaining wall, the Toronto Star reports.
Bystander Logan Tremblay said he called the police after he saw a teenager running through the bushes in the front yard of his home.
He said he saw an officer chase the teen in a car before pursuing him on foot.
"Before the cop could get him the kid went over the rail and over the gorge. He jumped in after him," Mr Tremblay said.
The suspect and officer are both believed to be alive, with one of the men critically injured.
A man believed to be the officer was plucked from the gorge by the rescue basket of a truck and then airlifted to hospital.
Rescue crews are still trying to recover the second individual but recent reports suggest he has died.
It is not known what led to the pursuit.