UPDATED 6.26pm: Christchurch police are appealing to the public to find three men who attacked two brothers early yesterday morning.

The two brothers have received fractures with one suffering a brain bleed, following an assault in Christchurch's CBD at the weekend.

The men, believed to be in their early twenties, attacked the pair on St Asaph St, between Colombo and Durham Sts around 1am on Sunday.

Both of the victims were seriously hurt in the assault, and one remains in hospital with a serious head injury, after being king hit by one of the alleged offenders.

The second man was treated in hospital for facial fractures, but has since been discharged.

The fight was broken up by security guards and the victim’s friends.

Detective Senior Sergeant Leairne Dow said they'd like to speak to any potential witnesses.

"It's a cruel event to two young boys who were just innocently walking through a car park in the central city."

Dow said they're also looking to speak to anyone who may have seen a silver Subaru in the area.

A police statement said one of the men is believed to be Caucasian, with ginger or brown curly hair, of large build and between 173cm and 180cm tall.

He was wearing a light-coloured button down long sleeve shirt, dark-coloured pants and dark-coloured shoes.

The other two men have been described as Maori. One is said to be of large build, and the other thin build.

They were both wearing dark-coloured clothing.

Police are urging anyone who witnessed the assault, or may be able to identify the men, to contact Detective Senior Sergeant Leairne Dow at Christchurch Central Police Station on (03) 363 7400, or report any information anonymously via Crimestoppers on 0800 555 111.