Rock thrown at police car: charge

A man has been charged after allegedly throwing a rock at a car driven by an off-duty police officer in Sydney.

A constable attached to Blacktown police was driving west on Richmond Road in Sydney's west about 10.30pm yesterday, when his vehicle was hit by a rock.

"A short time later another motorist's vehicle was struck by a rock at the same place," police said in a statement.

No one was injured.

Patrolling nearby, police allegedly saw a 21-year-old man throw a rock at a vehicle.

The man was arrested and later charged with throwing the rock, before being granted bail to face Blacktown Local Court on May 21.

The incident follows reports that a lump of concrete was thrown through a car windscreen on the M4 at Greystanes last week.

The 51-year-old man driving the car was struck on the head and also suffered abdominal injuries.