High-school students in London, Ont., are claiming police brutality after a young man was shot by a Taser as an officer attempted to break up a fight on Thursday.

The incident, which was recorded on cellphone video and later posted to YouTube, shows two youths who appear to be teenagers throwing punches on the street as a crowd of youths gathers around. A police officer runs toward the teens and fires the stun gun.

One of the youths engaged in the fight near Beal Secondary School drops to the ground, dazed and limp, and a voice off-camera repeatedly yells at the officer, "You shot him in the head! Why?"

Several students — many holding smartphones — are shown in the online clip, titled Police Brutality Cop Tazered 17 year old male hb beal.

The Canadian Press reported the two were both 17-year-olds.

Chris Tremblay, a youth who says he witnessed the incident, told CBC News he saw the fight and was surprised by the police response.

"He didn't even yell, 'Stop' and then he just Tasered the kid — like, just came up and Tasered him in the ear, and the kid was not all right," Tremblay said. "He was lying on the ground. He was not all right."

'It was unfolding very, very quickly'

London police admitted on Friday the weapon was deployed without a verbal warning but its police chief said the youth was assaulting the other with a chair.

The teen had wrapped a belt around his fist, punched the other teen and then used a chair to strike the other teen, Chief Brad Duncan said.

He said given the situation, the sergeant was justified in deploying the Taser without giving a warning.

"Clearly here it was unfolding very, very quickly," Duncan said.

Police said the teen was taken to hospital for injuries suffered in the fight, but not from the jolt of the stun gun. However, the boy's mother said he was treated for Taser-related injuries.

She also said her son was defending himself in the fight.

Tasered boy charged with assault

Provincial guidelines state that a Taser should not be used in sensitive areas, including the head.

London Police Const. Dennis Rivest said the investigation is in its early stages, and that questions about how the Taser was discharged are part of that investigation.

"I want to be cautious here and make sure that we have all of our information about what has taken place, and when we have all of those details, then we can talk further," he said.

The boy who was hit by the stun gun has been charged with assault with a weapon. The other boy, who goes to a different school, has not been charged and has been released from custody.

The Special Investigations Unit, which probes police action that results in injury, sexual assault or death, has said the incident does not meet its criteria for an investigation. Instead London police will look into the matter internally.

Angry students, meanwhile, have said they are considering holding a demonstration against police on Monday, saying officers are supposed to serve and protect, not hurt citizens.