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The video shows an employee of a security firm which provides services to South City Shopping Centre on Colombo St throwing a woman to the floor and pinning her down.
A shopping centre spokesperson said it is aware of the incident and the video which surfaced on Friday morning.
The spokesperson said the shopping centre has launched an internal investigation and notified police.
"We are aware of a security incident at the South City Shopping Centre that has been filmed and shared on social media," the spokesperson said.
"The incident appears to involve a woman who was previously trespassed from the shopping centre, an employee of the security firm contracted to supply security services to the centre, and another person trespassed from the centre videoing the incident.
"We have launched an internal investigation into the incident and the matter has been referred to police."
He said the security guard would be stood down during the investigation.
"We have asked our security contractor to stand down the employee involved while the incident is fully investigated.
"We are unable to comment further while the matter remains under investigation."
A police spokesperson said they responded to the incident after a report of two people behaving aggressively after an alleged shoplifting incident at a commercial premises on Colombo St.
"They left the premises before police arrived. Police conducted enquiries and took two people into custody."
Two 21-year-old women are due to appear in Christchurch District Court on October 26, charged with wilful trespass, and more charges are likely, the police spokesperson said.
The video was posted to the Christchurch Crime and Police Activities Facebook page.
It has been removed from the page but not before attracting a range of comments.
Said one commenter: "Good on him! He has done nothing wrong he's doing his job, cut him some slack! She however deserved everything she got, maybe she will learn to have a bit more respect and grow up!"
Another read: "She was inappropriate but they should be trained to handle these situations without brute force this is a full power trip."
"Looks like a human being who just literally has had enough ...I feel sorry for him, as he will undoubtedly see this, or be reprimanded and have to deal with it when he isn't feeling that in the moment reaction and adrenaline (sic)."