AN off-duty policeman has been bashed unconscious after attempting to stop a moped rider from the leaving the scene of an accident on the Sunshine Coast this morning.

Police are investigating the incident which occurred on Kingsford Smith Parade at Maroochydore about 5am.

Police say a traffic crash occurred involving a man riding a moped. The off-duty policeman attended the scene and tried to stop the rider from leaving.

Police allege the officer was punched a number of times, causing him to lose consciousness.

A woman who tried to help the policeman was then allegedly punched in the chest.

The moped rider fled the scene on the moped but crashed a short time later, breaking his leg.

The 28-year-old Caloundra man was arrested and transported to the Sunshine Coast University Hospital for treatment.

The police officer was transported to hospital for treatment of non-life-threatening injuries to his head.

Investigations are ongoing.