A young Christchurch woman and her mother are nursing a pair of black eyes after a woman tried to fight her way into their car in the early hours of New Year's Day.

Georgia Fergusson, 22, has posted images of their injuries on social media, alongside a video showing the end of the violent altercation with the unknown woman outside the Christchurch Casino.

Police confirmed an investigation was under way into the incident that happened at 1am that morning.

Acting Senior Sergeant at the Christchurch District Command Centre said police attended the "altercation between the victim and an unknown female" at 1.25 that morning.

"The matter is still under investigation," he said.

Miss Fergusson detailed the events that led up to what she described as an unprovoked attack.

She said her mother, Michelle Coker, had come to pick her and her boyfriend up at the end of their New Year's Eve celebrations.

"The woman in white had opened my mum's passenger door and I had tried to explain to her that it wasn't a taxi, it was my mum picking me up.

"That's when she punched me in the face."

Miss Fergusson said her mother then got out to come to her rescue and ended up getting punched in the face.

"As my mother was trying to get this woman off me, a man, who we assume was her boyfriend punched my middle-aged mother right in the face."

The video showed a woman in a white dress raining blows on Miss Fergusson who was screaming while on the ground. Meanwhile, her mother, in a yellow dress, was shouting and swearing as she tried to drag the woman off her daughter.

Eventually Miss Ferguson said two women, one being an off-duty ambulance officer, stepped in to help break up the fight.

She has shared the video around social media in the hopes of tracking down those responsible.

"Please share this with everybody you can," she said. "We need to find these people."

Miss Fergusson has also thanked those who have wished her and her mother well.

"My amazing mother and I would like to thank all the hundreds and thousands of people for all their support and well wishes. Thank you for helping spread the word. We really believe we will catch these scumbags."