Mandurah's Smart Street mall descended into chaos overnight, with a violent street brawl captured on video by a nightclub patron.
The shocking mobile phone footage shot at 2.15am shows more than 20 people involved in the fight, with security attempting to intervene.
Norma Jeans nightclub patrons are heard cheering and clapping from the balcony.
This comes after a man was stabbed two weeks ago on June 15, after police alleged an argument within Norma Jeans nightclub escalated to a street fight.
A WA Police spokeswoman said Mandurah Police were investigating the incident.
"Police have spoken to several people, who do not wish to make a complaint regarding this matter," she said.
"Mandurah Police will continue to make inquiries into the incident."