South Australia's Police Commissioner Grant Stevens has hit out at the "trend" of bystanders filming serious and dangerous incidents on their phones instead of offering help, in the wake of Melbourne's Bourke Street attack.

Key points: Grant Stevens says it is "not unusual" for "stupid acts" to be posted on social media

Grant Stevens says it is "not unusual" for "stupid acts" to be posted on social media His comments follow people filming the recent attack in Melbourne

His comments follow people filming the recent attack in Melbourne He is encouraging people to help, not film

Hassan Khalif Shire Ali, 30, crashed his car in the Bourke Street Mall before stabbing three men — fatally wounding Pellegrini's Espresso Bar co-owner Sisto Malaspina.

He was shot in the chest by police and later died in hospital.

Videos of the attack emerged on social media as the incident was unfolding in the heart of Melbourne on Friday afternoon.

Mr Stevens told ABC Radio Adelaide while videos could be useful evidence for police, he worried some people were choosing to film rather than offer assistance.

"We always caution people to consider their own safety when they're confronted with a situation like that," he said.

"But I think there's a new trend now, where people are more likely to stand on the sidelines and video an incident, rather than actually think about whether they could help.

"We all have an obligation to protect others in the community and I think that's slipping away a bit."

Mr Stevens said it was not unusual for videos of fights or other "stupid acts" to end up on social media pages, including Instagram account "Shit Adelaide".

In June video was posted to the social media page of a man climbing Adelaide's famous Mall's Balls.

Last month, video of an alleged assault on Hindley Street in Adelaide's CBD was also posted to the account.

"Every weekend there are behaviours, stupid acts and violent incidents [posted] but people aren't intervening — they're not stopping anyone from doing something," he said.

"We always caution people about making sound decisions if they're going to intervene in something… [but] maybe… people are now more interested in getting that bit of footage that's going to get them more likes on Facebook or Instagram.

"It's just an observation."

Commissioner Grant Stevens says video recordings had changed police work significantly. ( ABC News: Nick Harmsen )

Melbourne man Michael Rogers was dubbed "Trolley Man" after attempting to help police by pushing a trolley towards the attacker as he lunged at officers with a knife.

Mr Stevens said it was not yet clear whether his actions had been helpful to police.

"There's no doubt he was brave," he said.

"He certainly thought he was doing the right thing, but time will tell whether or not he was actually a help or a hindrance."

Police themselves under scrutiny from filming

Mr Stevens said the pervasive use of smartphones and video recordings had also changed police work significantly.

He said officers throughout the country were feeling more scrutinised than ever.

"It's a sad reality now that every time a police officer uses any level of force — which is an understandable part of the job — they're doing so with this understanding that they're probably being videoed," he said.

"We know that this [filming] is happening… so we do put out calls for people to provide footage that they've captured.

"We use social media as an investigative tool, but it makes our job harder in different dimensions as well.

"There are positives and negatives for everything."