AN ASDA security guard “knocked out” a “man threatening shoppers” inside the store, with shocking footage posted across social media.

The CCTV shows a grey hooded man approaching the guard, who has “security” written on the back of his jumper, at the entrance to the Shoebury Asda store.

When the man in grey approaches, the guard - in his 30s - punches him in the face.

It’s been reported that the man in the hoodie was threatening customers, although police have been unable to provide specific details.

Following the punch, the man’s knees buckle and he collapses on the fall.

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Asda has launched an investigation into the incident, and is “fully co-operating” with a police probe.

Colin Simpson, a friend of the security guard, said: “He’s a really decent bloke, and would not overreact over nothing.

“He told me he was threatening people with a knife., “People who were in the store should be shaking his hand.

“There’s no way he would have punched him for no reason.”

A witness helps the man to his feet, though he still struggles to keep his balance.

CCTV from outside the shop appears to show him swaying from side to side.

A spokesman for the supermarket said: “We do not tolerate violence in our stores and are investigating the incident in our Shoebury store as well as supporting the police fully with their enquiries.

“As this is an ongoing police investigation we cannot provide any further comment at this time.”

A spokesman from Essex Police, said: “We are investigating following an incident in Shoebury.

“We were called to the Asda store in North Shoebury Road to reports of a disturbance where a man in his 20s was assaulted.

“Please quote the crime reference number 42/212023/21.”