A student will face court today after a brutal road-rage assault on a 78-year-old in front of dozens of school children.

Te Atatu grandfather Jasmati Patel is this morning in an induced coma in a critical condition at Auckland Hospital after being attacked about 8am yesterday.

Family members were devastated and baffled as to why someone would hurt the much-loved father and grandfather. One of his grandsons, who did not wish to be named, was in complete shock.

"We are all a quiet family. We get on with our lives and our jobs. It has come as a shock. He did not deserve this," he said.

The boy described his grandfather as a friendly and quiet man who loved gardening, and kept to himself.

Police say the incident - which escalated in front of a large crowd of intermediate school children at a bus stop - occurred about 7.50am, after a minor collision between a 1997 BMW and a Nissan van on Carrington Road in Mt Albert.

They say the BMW driver - believed to be a 27-year-old Unitec student - leapt from his vehicle following the prang and struck the grandfather repeatedly. He then allegedly hauled him out of the van on to the road and continued the attack.

The car driver was arrested a short time later and taken back to Avondale Police Station, where he was charged with assault and questioned over the matter.

He is due to appear in Auckland District Court this morning.

Detective Sergeant Pete Steward of Avondale Police told the Herald the attack had been triggered by a "very, very minor" accident.

He said the man was in Auckland Hospital in an induced coma suffering "punch-in-the-head-type injuries".

"There's a fair bit of blood ... it's a serious injury."

Investigators were at the scene for almost five hours, finally removing both vehicles about 1pm.

Police would not comment as to whether the alleged offender was known to police or whether alcohol or drugs had played a part in the attack.

But police spokeswoman Noreen Hegarty said that would be "part and parcel of the police inquiry".

Gladstone Primary principal Dave Shadbolt was one of about five people who went to the school gates after hearing of an "incident" on the roadside. He said he saw an "older"man on the ground. "There was just a lot of blood. His eyes were closed, he was just breathing heavily."

Mr Shadbolt said he was aware of another man nearby, being dealt with by police, who had arrived at the scene within minutes.

"By the time we got there he was quite calm. He was close enough, but we weren't really looking at him. We wanted to make sure none of our children came past."

A long-time neighbour of the Patels, Rona Patterson, was appalled by the incident. "Poor old Mr Patel wouldn't hurt a fly," she said.

Mrs Patterson has lived two doors down from the Patels for 21 years and described him as a great neighbour and family man.

Police yesterday appealed for anyone who knew anything about the attack to get in touch on (09) 820 5786.

ADDITIONAL REPORTING: Rachel Tiffen, Isaac Davison and Lincoln Tan