Ambulance staff were shocked after discovering eggs and flour had been thrown over one of their vehicles while they were attending a medical emergency in Peterborough.
Paramedics were on call in Melford Close, Longthorpe, on Wednesday last week when shortly before 9pm a rapid response vehicle had its windscreen covered.
The “senseless act” was said to have resulted in the emergency vehicle being unable to respond to incidents for an extended time while it was being cleaned.
Police are now investigating the incident.
A spokesperson for the East of England Ambulance Service said: “It’s hard to understand why anyone would vandalise other people’s property, but when it happens to an ambulance vehicle while the crew is giving urgent medical assistance, it’s beyond belief.
“Rapid response vehicles are used to get to urgent calls quickly - they help save lives. Taking one off the road because of vandalism can therefore put lives at risk needlessly.
“If you know anything about this incident please contact Cambridgeshire police on 101 quoting crime number 35/26289/18.”
The spokesperson said “eggs, flour and other substances” had been thrown.