A New Zealand man is behind bars after admitting forcibly holding a fan heater to a young boy's face, causing disfiguring burns.

The unemployed man, 46, on Tuesday pleaded guilty in Christchurch District Court to disfiguring the child with intent to cause grievous bodily harm.

The summary of facts stated the man held the heater grill against the five-year-old's face because he was angry when the heater was knocked over and scorched the carpet.

Some of the boy's burns were so deep they passed through all his layers of skin.

Police examination showed burnt skin and tissue appeared to be stuck to the fan grill.

Suppression continues for many of the case details and the accused's name to protect his young victim's identity.

The boy was discharged from hospital after treatment for third-degree burns from his eyebrows to his chin.

His injuries will mean a long and painful recovery, including months of extensive skin grafts.

The man has been remanded in custody until his sentencing on November 13.