Three people have been arrested after a brawl in Wairoa early on Sunday in which police were attacked and a partygoer received head injuries.
Police say about 40 people had been at two parties in the Hawke's Bay town when a fight broke out between the two groups at about 2am.
They say officers who arrived at the scene had to call for reinforcements after a piece of concrete and glass bottles were thrown at them, smashing car windows.
Police say the rival party-goers were taunting each other and weapons included pieces of wood and a bat.
No police were hurt, but a man with head injuries was flown to Waikato Hospital on Sunday after his health deteriorated.
Four others were treated for minor injuries.
Police say the incident was not gang related, as they reported earlier and more arrests are expected.