A friend of two people shot by police in Christchurch last night - one fatally - say they had a troubled relationship

Police shot and killed the woman and critically injured the man, at a home on Clyde Road, about 11pm.

They say they were responding to reports a man was armed with a knife - and threatening to hurt himself and his partner.

Nathan Light met the couple at the local church, and says the pair had been in an on-again off-again relationship for five years, but were sorting their lives out.

Police say a critical incident investigation is under way, and they've advised the IPCA, as is standard.