The car's headlight's and indicators were damaged in the attack, the teenaged victim said.

A machete-wielding attacker beat up a pupil outside a school during a violent road rage incident in Auckland.

The 10-minute long attack on Monday morning only ended when construction workers pulled the man away.

The victim was left battered and bruised, and with marks on his head where his attacker had put him in a choke-hold.

"He kept yelling 'I'm going to break your ...neck'. It's not the sort of thing you expect to happen at 8.20am in the morning," the 18-year-old victim said.

The attack began on Murphys Rd when the teenager tooted at another car, which failed to let him into a line of traffic, almost forcing him off the road.

"I didn't really think too much off it, I just turned left and started driving down Ormiston Rd."

But the car caught up, got in front of him and slammed on the brakes.

"Then the guy got out and went to the back and pulled out this big machete."

He said the attacker swung the machete at the passenger door, narrowly missing his girlfriend.

"The machete hit the door, or it could have been really nasty."

The pupil managed to get away and headed towards his school, Ormiston Senior College.

"I thought it would be safe, that there would be heaps of people there. I was driving pretty crazy by them, dodging in and out of traffic."

But again the attacker got in front of the victim's car, and slammed on the brakes right outside the school, the teenager said.

The attacker jumped out, opened the door, and starting to punch the victim, who was in his school uniform.

He then reached over, undid the seatbelt, and dragged the teenager onto the road, where he proceeded to beat him up some more.

"I thought he was going to stomp me, so I was just trying to protect my head. He was twice the size of me. Then he got me in a kind of a choke-hold."

At the same time a woman was kicking the pupil's car, damaging the headlights and indicators, the teenager said.

Three construction workers ran over to stop the attacker - but he wasn't done.

"As they dragged him away he managed to get a good knee in."

The victim said the attack lasted about 10 minutes.

"That's a long time when you've got some massive guy trying to beat you up."

The attacker was described as a large Pacific Islander in his late 20s, driving an older model BMW.

An Auckland police spokesman said the incident had been reported and was being investigated.