CCTV has caught the moment a bus driver was viciously punched in the head by an irate passenger, who was then kicked in the back by the dazed driver in retaliation.

The incident, which occurred on December 17 on Queen St in the CBD, has resulted in the driver getting a formal warning by NZ Bus, while the assailant has never been caught.

Tramways Union boss Gary Froggatt said the company's actions were "heavy handed" and unfair.

Froggatt said drivers needed better training in how to deal with unprovoked attacks. He is appealing the warning and preparing a personal grievance case on behalf of the driver.

"I don't think he needs a warning. He just needs some retraining.

"It's not acceptable for passengers to do that and it's not acceptable for bus drivers to get involved in altercations with passengers.

"There should be more training and making sure drivers understand what they can and can't do in situations like this."

Alarmed passengers watch on during a physical altercation between a passenger and bus driver on Auckland's Queen St last month.( Photo / Supplied)

The footage shows a man in a hi-vis vest boarding the bus and scanning on with his hop card. Before the man takes his seat the driver pulls out, causing the passenger to lose his balance and hit his elbow.

The passenger then uses expletives before approaching the driver and punching him hard in the head.

The dazed driver stops the bus, then gets out of his seat and follows the passenger down the aisle. He grabs the top of two seats and swings his body towards the passenger, kicking him in the back with both feet.

An altercation then takes place between the two men in the aisle, with the passenger taking another swing at the driver which fails to connect.

Alarmed passengers watch the action unfold, with one man saying: "Call the police at once."

The passenger uses more expletives before pushing the emergency button and exiting the bus.

The bus driver, who received medical attention at hospital after the attack, has been off work on ACC but is preparing to return to work.

A police spokesman said officers had made inquiries into the alleged assault.

"Despite obtaining CCTV footage police have, as yet, been unable to identify the offender.

"Police have also been advised by the complainant that they do not wish to proceed further with the matter.

"The complainant's wishes have been taken into account and police have filed the matter, pending any further relevant information."

In a statement, NZ Bus chief operating officer Jay Zmijewski​ said the company did not comment on employment matters.

"In relation to this particular incident, there may be facts that are not known to you or the public, but as stated above NZ Bus does not comment on employment matters.

"NZ Bus takes the safety of our drivers, including the prevention of assaults very seriously. In this regard, we have procedures that drivers are required to follow in order to de-escalate a situation and reduce the likelihood of an assault occurring.

"These procedures have been well communicated and are supported by the Unions. We also conduct targeted de-escalation training."