A man involved in a charity boxing event is fighting for his life in hospital this morning.

Kain Parsons was critically injured in a match against former Canterbury and Tasman Makos rugby halfback Steve Alfeld during the Fight for Christchurch event at Horncastle Arena last night.

Police and emergency services were called to the arena just after 11pm last night. Parsons was taken to hospital in a critical condition.

A Canterbury District Health Board spokeswoman said the family was requesting privacy and would not be providing any comments.

According to his fighter biography, Parsons was a former builder who now worked in project management at Versatile Garages in Christchurch.

He was a "keen spectator" at the 2017 charity boxing event, and this year decided to give it a go and raise funds for the Conducive Education Canterbury, an early intervention programme for preschool children living with developmental delays and disorders.

His Givealittle page set up for the fight had raised nearly $3000 as of this morning, with a target of $5000.

Fellow boxer Mananui Ramsden told his thoughts were with the competitor.

He didn't see the fight itself as he was warming up.

"From all accounts, copped a very good, clean blow, and then landed very heavily, and that's about all I really know."

Ramsden said the event aimed to raise money for charity, not to hurt people.

He has a message for the Parsons family.

"Keep your heads up and your hearts big and certainly thinking of you. It's certainly not an easy time, and I;m certainly thinking of the whanau today."

Fight for Christchurch involved 18 amateur boxers fighting to raise money for two charities.

The fighters are described on the event website as "ordinary people, who have stepped up to do something extraordinary".

"One step at a time, one punch at a time, one round at a time, our contenders will shed sweat, tears and even a little blood to prepare themselves for their bouts."

Each boxer was championing either the Cure Kids or Conducive Education Canterbury charities.

The charity event has raised hundreds of thousands of dollars for Christchurch-based charities over the past eight years.