Adelaide's Westfield Marion Shopping Centre was put into lockdown on Sunday after reports of people with weapons inside the mall.
Images showed signs with the words 'Armed Offender' and a warning to 'Escape Hide Tell'.
Multiple videos posted to social media showed police storming the mall with firearms.
Police have since said the incident was triggered by reports of armed youths brawling inside the centre.
One shopper told Adelaide Now they heard a public announcement telling everyone to evacuate because there had been a 'weapon' on level 2.
"People were certainly panicked and running to all the exits,'' they said.
Another eyewitness said there was "mass evacuation and panic".
"Complete lockdown. Lots of people locked in the back of shops waiting for all clear," they wrote.
7News obtained footage of the moment the chaos started, showing two groups of youths fighting just before the lockdown started.
In an update, South Australia Police confirmed they'd received reports of two groups of young males fighting in the food court.
"Some people in the group were reported to have weapons," a spokesperson said.
"As a result of the incident, centre management activated an audible alert and evacuation alarm, and the centre went into lockdown.
"Numerous police resources including STAR Group officers attended the centre to commence a search for the groups involved in the initial disturbance.
"A thorough search of the centre was conducted including rooftops however the groups involved were not located.
"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."
South Australia Police said investigations are underway to find those responsible.
