SA Police to provide update on 'incident' at Westfield's Marion ...

Earlier, police said Westfield in Adelaide's south-west had undergone active armed defender training just a week ago.

In the video below, heavily armed police are seen running into the shopping centre as the incident unfolded.

Westfield Marion has released a statement, saying it will reopen for trade "as normal" tomorrow.

"Our team have been providing their full support to SA Police this afternoon who attended an incident at Westfield Marion," a spokesperson said.

"For a brief period SA Police were in full control of the site.

"SA Police have since advised it is safe for customers to leave the centre.

"We are not aware of any injuries.

"Westfield Marion closed at 5pm today, in line with normal trading hours, and will re-open for trade as normal tomorrow."

Here's some footage of witnesses speaking to the ABC outside the Westfield's Marion Shopping Centre.

Here's a video capturing the moment people inside the Westfield Marion heard it was safe to leave the shopping centre.

Video from inside Westfield's Marion Shopping Centre shows shoppers fleeing as brawling men triggered a lockdown.

Assistant Commissioner Scott Duval says police reaction has changed since the Bondi attack in April this year.

"These types of reactions to these incidents are very much influenced by incidents like Bondi," he said.

He said the reason the police exercised with Westfield was also closely linked to the incident.

"We have a fantastic relationship with these retailers and the exercising is what allows us to put in place a very good response."

Assistant Commissioner Scott Duval says the police response to the incident will be reviewed.

"There's always opportunities for improvement," he says.

"We always debrief our exercises and major incidents.

"Any particular issues that come out of these incidents will certainly be reviewed and we will be looking at our practices and procedures as I expect Westfield to be doing."

Assistant Commissioner Scott Duval has told the youth to "hand themselves in to police".

He said they "severely inconvenienced all shoppers at the centre".

"Perhaps they did not intend for this to occur but they need to understand the consequences of their actions and that those consequences involve people's safety," he says.

Assistant Commissioner Scott Duval said that no one was injured in the altercation of the group of boys.

He said that a 77-year-old woman may have fallen during the evacuation and suffered a fracture. 

A younger girl, who he believed was 14, also may have been injured during the process.

The Westfield in Adelaide's south-west had an active armed defender training with police a week ago, Assistant Commissioner Scott Duval says.

"What that does is highlight the practices we have in place with these major centres for this very type of incident, where the centre may go into its emergency procedures," he adds.

Assistant Commissioner Scott Duval says police already know the identity of the two victims, and the vision shows it was "not a random attack".

"The boys would appear to be known to each other but obviously we are in the early days of the investigation of the incident," he says.

 "As I say, the incident really involved three boys approaching another group of boys.

"We are not clear on the intention of that at this stage but I stress it does not appear to be a random attack, and it does not appear that the three boys were intending on targeting anyone else in the centre."

Assistant Commissioner Scott Duval says CCTV footage shows the first group of boys chased the second group through the Westfield into the David Jones store.

"That was the first part of our focus of where we put our specialist attention, to start clearing the centre to ensure the safety of all people could be insured," he says.

Assistant Commissioner Scott Duval says the youth are better classified as "boys under 18 years, of Caucasian appearance."

"They approached another group of boys and an altercation occurs," he says.

"The expandable batons are seen and at this stage we cannot discount any other weapons but we have reports that a knife may be involved."

Assistant Commissioner Scott Duval is saying SA police responded to reports of a fight between youth in the food court.

"We had information that it involves three of those offenders, some of them armed with expandable batons," he says.

"Police responded and by the time police had got to the centre, Westfield Marion had enacted their emergency procedures."

SA Police say they used multiple police resources including STAR Group officers to search for the two groups.

"A thorough search of the centre was conducted including rooftops however the groups involved were not located," police said

"Several shoppers who sought refuge in shops were safely escorted from the centre.

"Police are satisfied that there is no ongoing threat to the community."

They added that more investigations were being carried out to identify the groups.

We've just had an update from SA Police.

They says police received reports of "two groups of young males fighting in the food court area of the centre."

"Some people in the group were reported to have weapons," the statement said.

"As a result of the incident, centre management activated an audible alert and evacuation alarm, and the centre went into lock down."

Here's how one man, who was watching a movie, reacted to the evacuation.

"It must have happened really quickly," he told ABC News.

"It is one of those situations where you just grab your loved ones and move and get out and make sure everyone is fine.

"It is pretty confronting but at the same time you think, is is even real?"

Here's more from an eyewitness on the ground.

"Everybody is freaked out a little bit, people were distraught," one man told the ABC.

"We still don't really know what happened.

"I kept my family calm, but some other people sort of freaked out a little bit."