Detective Senior Sergeant Karen Simmons said officers responded to the incident at Richmond Village Green on the corner of Stanmore Rd and London St about 9.20am.
"Christchurch police investigating a serious assault in the city are seeking help from the public.
"The female victim was found seriously injured at the Richmond Village Green.
Police want to speak to anyone who may have information that would help with their investigation into what happened.
Hato Hone St John sent an ambulance and rapid response vehicle to the scene.
“One patient was assessed at the scene and transported to Christchurch Hospital in a critical condition."