An injured elderly woman's treatment was delayed after two youths slashed the tyres of a paramedic car.
The fast response vehicle was called to Spencerfield Crescent, Thorntree, Middlesbrough, early on Thursday to help the woman who had fallen.
She had broken her arm and while paramedics helped her two youths slashed the car's tyres with a knife.
The woman was then forced to wait for an ambulance. Police said such attacks put "lives at risk".
The boys were approximately 16-years-old, about 5' 6" tall and wearing dark clothing.
PC Nick Edgar, of Berwick Hills neighbourhood policing team, said: "The attack on this vehicle is particularly disturbing, as it shows a complete disregard for the elderly lady who needed hospital treatment.
"Causing damage to an emergency vehicle is dangerous and can put lives at risk."