A driver was left shocked after his car was hit by a rock hurled off an overpass over the Spine Road.
He was driving along the A189 towards Ashington on Thursday afternoon when a man standing on the overpass at the Cambois turn threw a rock which hit the bonnet of the BMW.
The person responsible was in a group of three or four people at the time.
PC Ian Taylor said: "This sort of reckless behaviour is extremely dangerous and could easily have resulted in serious injury to the motorist and other road users.
"Extra patrols will be carried out in this area to reassure people and prevent further incidents. If anyone sees any suspicious behaviour in this area please report it to us straight away."
Police are appealing for anyone who was in the area and who may have seen or heard anything suspicious to ring 101, quoting reference number 465 of 24/11/16 or the independent charity Crimestoppers on 0800 555111.
Police are also appealing for witnesses after the tyres of a car parked on the driveway of a car on Delaval Crescent, Newsham, were let down. The offender returned on two separate occasions and scratched the off-side panel and smashed the front nearside headlight, causing substantial damage.
The incidents happened between 8pm on Monday, November 21, and 8am, on Thursday, November 24.
Police are appealing for witnesses, anyone who was in the area and who may have seen or heard anything suspicious, is asked to contact police.