A man has been stabbed in Taumarunui with what police describe as "a large knife", which was left embedded in his upper chest.

Friends rushed the 18-year-old to the local hospital before he was flown to Waikato Hospital, where he was in a stable condition, police said on Sunday.

They did not say when and where the attack happened.

An 18-year-old Taumarunui man has been arrested and is being held in custody.