Police arresting a 23-year-old Sudanese man out the back of a Melbourne chemist in 2016 kicked, punched and bashed him with a baton, security footage has revealed.

The man was suffering a psychotic episode at the time, and had charged into the chemist, flipping a sign over the counter and robbing the store, video obtained by The Age showed.

He was restrained after heading down a hallway behind the counter by another customer, who did not hit him. Footage shows when police arrive, the man is punched around his head, kicked, and jabbed harshly with the end of a baton.

After he is placed into handcuffs following the brutal two-and-a-half minute ordeal, the officer who had hit him previously goes in for a final, insulting blow.

He is helped up by another policeman and once on his feet, immediately turns back and stomps on the man's back.

Pictured: A Victoria Police officer is seen on CCTV footage stomping on a man's back after he is handcuffed for robbing a chemist

The African man's legal counsel, Natasha Woland, told The Age she was 'absolutely horrified' when she viewed the CCTV footage.

'There is no way a reasonable person would find the use of force proportionate,' she said.

Her client was having a psychotic episode at the time of the robbery, and in the lead up to his arrest, he had attacked bystanders and threatened the man working at the chemist with scissors.

In October last year, the man, who has asked to remain nameless, pleaded guilty to his crimes and was jailed for two years and nine months.

He was originally also charged with resisting arrest and assaulting police, but after the CCTV became available, those charges were quietly dropped.

Before the man was handcuffed, he was punched around his head 11 times by the officer, kicked and jabbed three times with the officer's baton

The man, 23 at the time, had stormed into a Preston chemist armed with scissors (pictured). He had attacked other people and was having a psychotic episode. Members of the public managed to restrain the man without using violence before police arrived

The violent arrest crossed the desk of the Professional Standards Command, Victoria Police's ethics and integrity unit. No action was taken.

A spokeswoman for Victoria Police told Daily Mail Australia on Thursday the force had now launched an investigation into the actions of the arresting officer.

'The CCTV footage of an arrest in Preston in 2016 is deeply concerning,' she said.

'With the agreement of IBAC, Victoria Police is now in the process of reviewing the CCTV to assess whether the conduct depicted is in keeping with established operational standards.

'Once an assessment has been completed, which measures the actions of the police officers against the policies and standards we set through our training at the Victoria Police Academy, then the case will be referred back to AC Luke Cornelius as the Head of Professional Standards for consideration as to whether any interim actions should be taken, pending the outcome of an investigation by IBAC.

'Initial actions can range from the temporary re-assignment of an officer through to suspension.'

While dismissed at the time of the arrest, an investigation into the actions of the officer has now been launched by Victoria Police

More recently, a disability pensioner was pinned down by six policemen, repeatedly hit with a baton, capsicum sprayed and blasted with a garden hose outside his home.

In footage that has shocked Australia, Victorian police officers are heard yelling at John to 'put your f***ing hands behind your f***ing back' and asking if 'he liked' the smell of pepper spray after it was used on his face at close range.

John was struck in the leg with a baton six times, before he was handcuffed and sprayed with a hose on the front lawn of his Melbourne home.

In the clip he is heard asking his tormentors: 'Why are you doing this to me?'

Former judge Michael Strong, who was the head of Police Integrity before it was absorbed by IBAC, told ABC's 7.30 serious complaints like those made about the Preston arrest need to be investigated independently.

More recently, a disability pensioner was pinned down by six policemen, repeatedly hit with a baton, capsicum sprayed and blasted with a garden hose outside his home

'The only way you could remove all conflict of interest is to have every complaint against police investigated by an independent agency,' he said.

'I would like to see more of the more serious complaints investigated by an independent agency - but that's a resourcing issue.'

Luke Cornelius from the Professional Standards Command of Victoria Police told the program any use of force such as that shown in the chemist arrest would require a 'robust' explanation.

'That force [punching a suspect in the head] would only be justified in circumstances where the police officer had made the assessment and this is a reasonable person's assessment, made the assessment that the use of that force was necessary in order to prevent imminent injury to that police officer, or some other party,' he said.

'Look, kicking anyone in the head, particularly while lying on the ground, would demand very close scrutiny and a very robust explanation and justification.'