UPDATED 3.10PM: A 36-year-old man who was king hit outside Denny's in south Auckland remains in a critical but stable condition in Auckland Hospital. 

Police say the man was seriously injured when he and a friend were challenged to a fight by a group of men in Manukau early Saturday morning. 

He's undergone surgery at Auckland City Hospital, and family members are at his bedside.

His mother has arrived from Australia.

Detective Inspector Uraia Vakaruru said the victim and his friend were walking into a Denny's restaurant at around 3.20am when a fight broke out.

"They have been confronted by a group of three to five Pacific men, [in their] late teens or early twenties. They've been challenged to a fight and the victim has been king-hit by one of these men."

Police want to hear from anyone who witnessed the fight.