A prolonged struggle between a suspect and a Toronto police officer — seen in a video posted online on Monday — shows an officer making a lawful arrest despite "dangerous" levels of interference by members of the public, according to police officials.

But the person who posted the 16-minute video claims it shows the result of an unprovoked assault by an officer who was discriminating against black people while standing guard at the liquor store near the Sheridan Mall.

This is dangerous behaviour. –Toronto police spokesman Mark Pugash

The video was posted on Facebook by a Hamilton-area man who claims he and a friend were at a Liquor Control Board of Ontario store near Jane Street and Wilson Avenue when a confrontation between the officer and a young black man quickly escalated. Police officials say the officer, who was on paid duty for the LCBO, was trying to make a lawful arrest after the suspect struck him.

Ajith Thala says he and his friend saw the officer stop the man from entering the store.

Moments later, "the officer was punching the gentleman and tackled him down aggressively with his knees on his neck," Thala wrote.

The scene that followed, as seen in the video, was tense and chaotic. The officer, who is white, is seen perched on top of the struggling suspect while a number of other people shout for him to be released. The language is often profane.

The officer appears to be calling for backup while attempting to handcuff the man. He is heard shouting at the crowd to get away, and at one point wipes blood from a cut on his head.

One bystander in particular, a man wearing a Toronto Blue Jays jacket, tries to pull the officer off the suspect. He and the officer have a number of heated exchanges, though the exact words are hard to make out.

After about four minutes other officers arrive, but confrontations and angry words from both sides continue.

None of the people in the video have been identified.

Lawful arrest

Thala claims, prior to the incident, the officer was "intimidating" any black people who came into the store.

The arresting officer is heard shouting at the crowd to get away, and at one point wipes blood from a cut on his head. (Ajith Thala/Facebook)

Police spokesman Mark Pugash says the officer barred the man, who was acting "fidgety," from entering the store. The officer asked for the man's ID and was about to issue a trespassing notice when the man allegedly struck him, hitting his vest.

He was then arrested for assaulting an officer. During the struggle the officer's head was injured, Pugash says in a statement.

"At least one person in a crowd of people attempts to obstruct the arrest, which is a criminal offence," Pugash says, apparently referring to the man in the Jays jacket.

"What is especially concerning is that members of the public shout down an officer trying to make a lawful arrest and try to free the person he has in his custody," he says.

"This is dangerous behaviour and troubling as the people in this crowd seem to want to take the law into their own hands."

The suspect, a 25-year-old man of no fixed address, has been arrested and faces a charge of resisting arrest and assaulting a police officer. Police say the incident occurred last Friday at 4 p.m. ET.