A police officer has been injured trying to break up a crowd in Sydney's north.
Police were called to Foxglove oval at Mount Colah around eight o'clock last night after reports from residents of a large group of people loitering in the area.
On arrival police broke up the crowd - but were called back an hour later when a bonfire was lit - the same group had returned.
The fire was extinguished - police began dispersing the crowd when some began throwing rocks at them.
A police dog squad officer was struck on the forehead - he was treated by ambulance crews for a laceration and swelling.
The riot squad was brought in to control the situation - police have vowed to increase patrols of the area as they look for the offenders.