A shopper who filmed Sydney shopping centre attacker Joel Cauchi walking through Westfield armed with a knife has spoken of his disbelief at what happened.

Cauchi, 40, stabbed six people to death at the Westfield Shopping Centre in Bondi Junction on Saturday (13 April), before he was fatally shot by a police officer.

Video footage shared online appears to show many people fleeing as a knife-wielding Cauchi walked through the shopping centre and lunged at people.

Rohan Anderson, who filmed some of the footage, said: “When I took my footage it was about 15 seconds maybe before he was shot by the police officer and he’d already killed a number of people at that point.”