A Christchurch community devastated by a random knife attack has been gutted by confirmation the accused killer is a mental health patient on community leave

Laisa Maraia Waka was randomly attacked in Sockburn by a stranger wielding a knife on Saturday.

Canterbury DHB has launched a review into how the 37-year-old man was allowed out into the community.

Waipuna Halswell-Hornby-Riccarton Community Board member Mark Peters says a close look into how mental health patients are cared for, is needed.

He says it shouldn't happen in any community - and to leave those facing mental health challenges in a situation where this happens, is tragic.