Police say this 23-year-old man was punched in the head and hit with the steel rod.

People in a Bay of Plenty petrol station got the fright of their lives when a man walked in last night with a bar sticking out of his head - and they realised it wasn't a costume.

"I was like, 'Man is this a TV show? Is this guy for real?'" Katikati Caltex owner Lester Gray told 3News.

The man was attacked by a group of people last night in the town .

The 23-year-old man had been sitting in his car on Clive Rd in Katikati, 40km northwest of Tauranga, just before midnight when two men and a woman approached the vehicle, Detective Sergeant Daryl Brazier said.

The group spoke briefly with the man before one of them punched him in the head. He then attempted to drive off but was hit in the head with an iron bar, which became lodged in his head, Brazier said.

The man went to a local petrol station for help.

"He just walked in with the rod in his head and I was just like, 'Is that a drum stick in your head?'" says witness Dylan Shea told 3News.

"And he was like, 'Nah, it's a rod.

"It looked like a Halloween stunt where people wear those Halloween costumes over their heads, but it was pretty real when he turned around and blood was coming down the side of his head," Gray told 3News.

It was not yet known what provoked the attack, police said.

The man was calm and coherent, they said, and asked the petrol station staff to call police instead of an ambulance.

It was not yet known what provoked the attack, police said.

The man was taken to Tauranga Hospital to have the bar removed, before he was airlifted to Waikato Hospital in a serious but stable condition.

The result of the attack could have been much worse, Brazier said.

"He was very, very lucky.

"If that hits him in another part of the head then it could very easily have killed him."