Dramatic video has emerged of a Victorian police officer stomping on the back of a handcuffed African-Australian man.

The man, who was having a psychotic episode, had assaulted several people before trying to hold up a Melbourne pharmacy armed with a pair of scissors in 2016.

He was repeatedly punched, kicked in the head, and hammered with a baton during the arrest.

Sorry, this video has expired CCTV footage shows police punching, kicking and stomping on a man during his arrest.

A subsequent internal police investigation cleared police of using excessive force.

The video has come to light on the same day as separate footage emerged showing police allegedly assaulting a disabled pensioner on his front yard during a welfare check.

The videos raise new concerns about the use of force by Victorian police and the system that deals with complaints against them.

Internal inquiry clears police

The 23-year-old had been on a rampage on High Street in the Melbourne suburb of Preston.

After assaulting a passenger on a bus, he attacked three pedestrians, including a man in his 80s.

He then walked into the pharmacy which he attempted to rob.

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Bystanders tried to take him down, with one receiving a wound to the head.

The CCTV footage, obtained by The Age, shows police struggling to handcuff the man after he had been disarmed.

But it also shows a police officer repeatedly punching the man, kicking his head, hammering him with a baton, and stomping on his back.

The offender later pleaded guilty to armed robbery and assault charges, and is currently serving a jail sentence of two years and nine months.

Bringing violent offenders like this under control is difficult and dangerous for police.

It is at moments like this when they must decide, in the heat of the moment, how much force is reasonable to bring a situation under control.

On that day, the man's lawyer said, police crossed the line.

Victoria Police's Professional Standards Unit disagreed. It found the actions of police were appropriate, and in accordance with the law.

But on Tuesday, Victoria Police said the incident was being investigated by the state's Independent Broad-based Anti-Corruption Commission (IBAC).

"I acknowledge that there has been a diminution in confidence in our community in police complaint and accountability processes," Assistant Commissioner Luke Cornelius, the acting head of Professional Standards, said at a press conference.

"It is clear to me that both Victoria Police and IBAC need to do more to recover that confidence, increase transparency and engage more effectively with community advocacy groups that are seeking to assist clients who have very serious concerns about police behaviour and conduct."

Assistant Commissioner Cornelius said he was looking forward to the "introduction of body-worn cameras, which are to be worn by all operational police officers when conducting their duties".

"That will make available to us footage at the time the incident occurred, which will allow us to assess whether or not in all the circumstances our conduct in particular cases has been appropriate."

'He was face down, he was disarmed'

Lawyer Natasha Wolan says the police complaints system needs review. ( ABC News )

The man's lawyer, Natasha Wolan, says the force used on her client was excessive.

"Police are confronted with violence every day. It's a very difficult job," she told 7.30.

"But he was face down, he was disarmed, and at that stage I think the force was excessive.

"He suffered significant facial injuries, most of his teeth were snapped, he's got ongoing back issues. He was taken to hospital after the incident because he was deemed not fit enough to be in police custody."

She says the overall complaints system needs review.

"I find it problematic that despite there being very clear CCTV footage, my client's case wasn't substantiated," she said.

At the time, the Victoria Police internal investigations unit, known as the Professional Standards Command, was headed by Assistant Commissioner Brett Guerin.

In February he was forced to quit in disgrace after he was found to have used a fake identity to post violent and racist rants online, referring, among other things, to "jigaboos" wanting "the lash".

Read the written statement from Victoria Police.