Shoppers whose Saturday afternoon turned into a gruesome nightmare have described the fear and desperation as they ran for their lives in one of Sydney’s biggest malls.

At about 4pm, the sight of crowds running and screaming in Bondi Junction Westfield alerted others that something awful was unfolding.

A 40-year-old attacker was moving through the multi-level complex, picking out his victims and leaving behind a bloody trail.

People were stabbed to death or horrifically injured inside the busy shopping centre by the knife-wielding assailant who was seemingly on a “rampage”.

One witness told the ABC he saw a man in a green shirt start stabbing others “indiscriminately”.

“[We just heard] screaming, screaming and it didn’t seem that long before we heard ‘boom boom boom’ of the gunshot and we thought, ‘We hope it’s the police,'” he said.

“[A person] is dying 10 metres away … I grabbed towels and there were three people dying around me.

“It was just carnage.”

Some witnesses ran for safety inside shops that closed their doors to protect those seeking refuge inside.

But that meant others were locked out and one witness, Kelly, told the ABC: “All the shops shut their doors. We couldn’t get in, they wouldn’t let us in. We just ran down the fire escape.

“I thought I was going to die. I thought we were going to be shot and killed. We thought he had a gun. We didn’t know it was a knife.”

Another man told the ABC: “They just said run, run, run someone’s been stabbed.”

“(The attacker) was walking really calmly like he was having an ice cream in a park.

“And then he went up the escalators … and probably within about a minute we heard three gunshots,” he said.

Tactical Response officers outside Westfield Bondi Junction. Photo: AAP

Other witnesses told of grabbing their children and running from the centre along with hundreds of other people.

Another witness told 7News the responding inspector had saved lives.

“If she didn’t shoot he would have kept going and I don’t know how many more he would have done,” he said.

-with AAP