Mr Berking said the man saw the group approaching and ran off.
Mr Berking tended to the woman - who was very upset and had obvious facial bruising and strangulation marks around her neck - while his friend Barrie Olsen, 36, followed the man.
Mr Olsen said the man ran towards the McDonald's restaurant and took off the blue overalls he was wearing, throwing them into a rubbish bin.
The man then tried to mix in with a group of teens who were standing near the library's steps, he said.
"By the time [Mr Berking] had rung the police, my other friends came around the corner and I called them over, this all happened in about two or three minutes, then we all just completely surrounded him pretty much.
"He realised he was out numbered and took off and ran away, and we all ran after him."
The man then ran towards the nearby Denny's restaurant.
"He tried to do a loopdey-loop around a van and ran back towards the road towards where I was standing and I managed to kick his legs out from under him and he fell over and the rest of the boys piled on top of him."
Police showed up soon after and the man was arrested and charged with assault with intent to rob.
He was due to appear in Waitakere District Court today.
Waitakere Police Area Commander Inspector Scott Webb praised the men's actions.
"The way they managed to co-ordinate themselves, call police, assist the victim and detain the offender was very impressive and we'll be looking at a way to formally recognise their efforts.
"This was a very frightening, random situation and I am sure the public will be reassured that the alleged offender has been arrested and put before the courts."
The victim received medical treatment for her injuries.
