A crime scene has been established after an officer was injured during the arrest of a teenager in Marsfield overnight, NSW Police say.
About 10pm today, a Dog Squad officer was patrolling the vicinity of Balaclava Road and Epping Road when he came across a person acting suspiciously.
The officer stopped his vehicle on Epping Road and approached the youth who allegedly became aggressive.
As a result, the officer attempted to arrest the youth with the assistance of two officers from Ryde Local Area Command who were patrolling nearby.
During the arrest police will allege the youth kicked one of the Ryde officers in the face causing him to fall and hit his head on the road.
The Constable suffered serious head injuries and was taken to Royal North Shore Hospital where he is listed as serious.
The 17-year-old was taken Ryde Police Station where he is assisting with inquiries.
Detectives from Ryde Local Area Command are continuing their inquiries.
Police are urging anyone with information in relation to this incident to call Crime Stoppers.