Passersby thwarted a brazen robbery and assault in central Auckland on Wednesday afternoon.
A witness to the incident said he saw a young woman snatch a phone off a stranger and bolt down Lower Albert St just after 4.30pm.
Walking home from work, he said he saw a woman wearing a jacket with her hood up run up to two other young women.
Thinking she was about to clap a friend on the back, the bystander instead saw the woman grab the stranger's phone and shoot off down the street, as he heard a scream of 'Somebody stop her'.
"It just came out of nowhere," the bystander said.
"Another member of the public braced herself and tackled the thief to the ground."
The woman who tackled the thief smashed her head on the concrete as the tangled pair fell to the ground but was able to throw the phone back towards its owner, he said.
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The incident appeared to be over, until the thief and her friend continued to follow the two women, now trying to get away.
Calling the police, the bystander followed the women, who continued to be harassed down the busy inner-city street.
One of the aggressors punched one of the two girls trying to flee them, he said.
"It was a hard punch, I saw her head knocked back."
At a nearby crossing, construction workers who had also witnessed the drama got involved and tried to block the aggressors from those trying to escape them.
Police quickly arrived and caught up with the perpetrators, the bystander said.
The bystander said it was a "horrible" thing to witness.
"She was an international student, which made me feel more horrible about it all," he said.
He assured the shaken student that this wasn't a normal thing that happened here.
Her friend, who was punched in the face, was bruised, but seemed alright, he said.
A police spokeswoman said the woman who was assaulted did not require medical treatment.
"Two people were taken into custody," she said.
The bystander said the "silver lining" of the experience was seeing strangers band together.
"For me, the takeaway was how quickly everybody around helped out: one random lady who wasn't involved, the construction workers, Police showing up quickly.
"If you try to rob and assault someone in the middle of Auckland city, you're not going to get away with it," he said.
"Everyone involved in stopping this did a really great job."