Drivers are being told to remain vigilant after reports of people hurling objects at traffic from motorway bridges.

Kent police has condemned the "stupid and malicious" crime, and warned offenders will face serious repercussions if caught.

So far this year there have been 15 reports of items thrown at traffic between junctions 4 and 5 of the M20, and from crossings over the A228 at Snodland and East Peckham.

Signs have been fixed to bridges which cross parts of the motorway in West Kent, warning people they could face up to seven years in prison and fines of £1,000.

Notices have also been secured to crossings above the A228.

Tonbridge Chief Inspector Gill Ellis said: "I cannot stress enough how dangerous it is to throw objects from bridges.

"Throwing anything at a moving vehicle is incredibly stupid and also malicious. It could easily kill someone, especially if they are travelling at high speeds on a major road.

"Fortunately reports of this nature are still rare, but those who commit such crimes will face serious repercussions.

"We also want motorists to be aware that incidents such as this are occurring and to remain vigilant."

In July 2010, a 47-year-old man died following a collision involving a lorry and a pick-up truck on the A20 Swanley interchange, after it was reported that stones had been thrown at the lorry.

CCTV cameras have also been installed to monitor locations.

Chief Insp Ellis added: "We will be monitoring the cameras and will arrest anyone we find carrying out these malicious acts. Visible patrols have been increased in vulnerable areas, which will be making regular checks for any suspicious behaviour.

"We are also working in partnership with local schools to inform and educate pupils of the dangers and penalties. I would urge parents to also ensure their children know the dangers and consequences of throwing objects onto the highway."

Contact the police if you see anything or have any information by dialling 101, or 999 in an emergency. Alternatively, if you wish to remain anonymous, call Kent Crimestoppers on 0800 555 111.