Scared shoppers were locked in shops, while others ran to escape, amid the emergency response at Westfield Marion.
Specialist police were called to at 2.50pm (local time) after initial reports three young men allegedly approached another group of youths in the food court and were reportedly armed.
“Everyone was running for their lives,” shopper Janet Raphael, said.
Centre management activated an alert and evacuation alarm, and the centre went into lockdown.
Specialist police were sent to the centre to ensure the safety of shoppers, police said.
“At that time, we had information that the fight involved three of those offenders, some of them armed with expandable batons,” SA Police assistant commissioner Scott Duval told media.
“In terms of the incident, I have looked at the CCTV, it involves three youths and I will call them boys under 18 years of a Caucasian appearance.
“They approach another group of boys and an altercation occurs.
“Expandable batons are seen and at this stage, we can’t discount any other weapons but we do have some reports a knife may be involved.”
Duval said police believe the three boys chased the other youths through the centre and went into David Jones.
Duval said police believe the boys knew each other and it was ”not a random attack”.
Witness Lily Poulton said one of the boys “opened the baton to the side and just started yelling and that guy just got up and sprinted through everyone in the food court.”
Terrified crowds of Sunday afternoon shoppers fled amid alarms and emergency announcements.
Dozens hid inside shops and others were evacuated to a roof as alarms sounded.
Armed officers could be seen running through the centre.
“It was just really scary,” one shopper said.
“It was like a movie, everyone was screaming,” shopper Alyssa Leopold, said.
People at the cinema were evacuated from a fire escape, and worried families were separated in the chaos.
Vicki Evangelou said one of her daughters was upstairs and two others were in other shops.
“They’re extremely worried and concerned, we’ve had to update them through the phone.”
Tom Workman said people were “pretty panicked” to get out the door.
Those inside shop were kept there for multiple hours as officers told them they were hunting two offenders.
“My partner and I were in David Jones near the jewellery section and we heard someone over Westfield (speakers) say ‘this in an emergency’,” another shopper told 9News Adelaide.
“Next minute the David Jones security doors went down.”
It is understood two shoppers were injured during the evacuation, including a 77-year-old woman who fell and suffered a fracture, along with a teenager girl.
Police are investigating the incident and speaking to witnesses.
”We have investigators here trying to make sure the information we had can be verified in some way,” Duval said.
“We’re still very keen to speak to the three boys who instigated the incident.”
The incident came 10 days after police were involved in a major training operation at the shopping centre in which they rehearsed the response to a “potential violent scenario”.
A Westfield spokesperson said the safety of customers, business partners and people is their “highest priority”.
“Our team have been providing their full support to SA Police this afternoon who attended an incident at Westfield Marion. For a brief period SA Police were in full control of the site,” the spokesperson said.
Shops will open as normal tomorrow.
The lockdown caused traffic congestion as hundreds of cars tried to leave the centre at the same time.
The shopping centre is one of the largest in South Australia and has more than 340 stores.