Thugs smashed up three police vans while officers were carrying out a knife-sweep in Salford.
The windscreens were smashed and the tyres were burst by the vandals while the vehicles were left unoccupied on Friday afternoon.
The incident took place on Heath Avenue, near the River Irwell, at about 4pm.
No one was injured and no arrests have been made.
Police are now appealing for information about the incident.
Chief Insp Ben Ewart of GMP’s Salford division said: “Our officers were out helping the community by doing great work removing knives from the streets only to come back and find that their vans had been vandalised.
“We have recovered the vans but they will have to be sent for repair before they are able to return to the roads as emergency vehicles.
“This behaviour is completely unacceptable and it will absolutely not be tolerated.
"Anyone with any information at all should contact police as soon as possible.
“Despite this incident you will continue to see patrols in and around the area as our officers carry out their positive work within the community.”
Anyone with any information is asked to call police on 101, quoting incident number 1908 of 21/02/20.
Reports can also be made anonymously to Crimestoppers on 0800 555 111.
