An "outgoing" young woman remains in a coma following a brutal attack in which she was punched in the throat after a Christchurch music festival.

Amelia Rayner had her trachea, or windpipe, crushed when she and her partner were attacked after leaving the Electric Avenue festival at Hagley Park about 11.15pm on Saturday.

Amelia's mum, Barbara Rayner, told the Herald her 29-year-old daughter is due to have further surgery to alleviate pressure on her airways tomorrow, as doctors keep her in an induced coma.

Barbara said she received a phone call about 11.15pm from Amelia's partner, who said, "we've been attacked, Amelia's come off worse than me".

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Barbara was told by surgeons her "outgoing" daughter was a "very lucky girl" to still be alive, but concerns remain over permanent damage to Amelia's speech.

"The surgeon said it was marginal, it could've been fatal."

She said the attack, which occurred near Park Terrace and Salisbury St, "took [the couple] by surprise".

"They don't know why they were attacked - [the attackers] took Amelia's hat to start and maybe something was said between them? But no one deserves something like this to happen to them."

Barbara said Christchurch has developed an "underbelly" of crime and attacks in recent times.

A police spokeswoman said police were investigating an assault after the festival.

"We don't have a description of the offenders at this stage but we will be talking to the victims as soon as we are able to in order to get a description and any other information they can provide," she said.