The man police are searching for after a bus driver was assaulted on the Sunshine Coast. Credit:Queensland Police Service

A 74-year-old bus driver has been knocked out after a one-punch attack by a fare-evading passenger on the Sunshine Coast on Thursday morning.

Police are appealing for public help to find the attacker, who is thought to be a teenager.

A male passenger boarded the route 631 bus at the Nambour bus terminal about 9.10am and got into an argument with the male driver after refusing to pay the fare.

The confrontation turned violent when the fare-evader punched the driver in the head once, knocking him unconscious. He was taken to Sunshine Coast Hospital for observation with non-life-threatening injuries.