A 31-year-old man has been arrested after assaulting a police officer on Auckland's Karangahape Road overnight.
Police said officers were dealing with a group fighting at about 3:30am, when a person who was not involved in the initial incident come up to the officer and hit them from behind.
Other bystanders and security guards intervened to help the officer and catch the man who had hit them.
The police officer was hospitalised suffering a serious concussion and is in a stable condition.
"The behaviour displayed by this man is unacceptable," police said in a statement.
He is to appear in the Auckland District Court on Monday.