Amelia Rayner, left, is now out of hospital and recovering.

A woman who "wouldn't hurt a fly" is in an induced coma after an attack at a Christchurch music festival.

Amelia Rayner, 29, allegedly had her trachea crushed after being punched in the throat while leaving the Electric Avenue festival with her boyfriend, about 11.15pm on Saturday.

Rayner's mother Barbara said her daughter was crossing the Armagh St bridge when three men approached and took her hat.

"She went and grabbed it back and her boyfriend may have said something to the guys but then that was that.

"They get up the road a wee bit, to the corner of Park Tce and Salisbury St ... The three who had originally taken the hat [and one other] just took to [Amelia's boyfriend]."

Barbara Rayner said Amelia went to help her boyfriend but "came off worse".

"This is so close to being a homicide. The hospital thinks she was within a hair-breadth of dying. She was very, very lucky."

Chris Rayner, Amelia's brother, said she had to be operated on immediately in order to clear her airway.

"She is currently in the intensive care unit and breathing on machines, but sedated with a balloon in her throat to stop her airway collapsing as the swelling resides."

Rayner's boyfriend was having trouble walking and was "very sore" but otherwise unharmed, Barbara Rayner said.

"He was so busy caring about her that he's only been looked at by a doctor [on Monday]. He's bruised and has rashes from the gravel."

A Canterbury District Health Board spokeswoman confirmed Rayner was in a critical condition in Christchurch Hospital.

Police were looking for four men between 5'11" and 6'1" tall, but would be seeking more information from the victims, a spokeswoman said.

"The police at the scene called the ambulance. The woman reported being punched in the throat and was struggling for breath.

"It's been assigned to the crime squad to investigate ... We'll be talking to the victims more."

Barbara Rayner said she hoped someone who saw the incident would come forward with any information that could help police.

"She wouldn't hurt a fly. She's the last person you'd expect this to ever happen to. She's very kind and very outgoing, friendly young girl.

"I think there was a lot of people around who may have seen something and not realised how serious it was."