An ambulance could not respond to an emergency call in Chorley after vandals hurled a heavy cobblestone through its windscreen.
Ambulance bosses have slammed the culprits, warning they could have put lives at risk.
The attack on the vehicle, which was parked outside Chorley Ambulance Station, Highfield Industrial Estate, took place at around 2.40am on Sunday.
Another ambulance had to attend the emergency, an assault.
Tommy Leigh, assistant sector manager for Lancashire Ambulance Service, said: "Someone could have lost their lives through that.
It is just vandalism at its worst.
"We are out there to help the public and don't really expect them to retaliate in that way."
Mr Leigh said he would now be pressing his bosses to install CCTV at the ambulance station.
He said: "The vehicle was parked outside the station for the purpose of a response. If you put it in the garage it takes time to open the doors.
"On this particular night the crew then went out to respond to an emergency call to find the windscreen had been smashed and a large boulder on the floor.
"Their action then was to notify control, they said they couldn't respond to the emergency. Following that they notified the police who came down."
Mr Leigh said it was the first attack of its kind on the ambulance station.
"We don't have a lot of vandalism around the ambulance station, they don't seem to target ambulances on the station. We have it outside on calls where youths can be threatening.
"It is disturbing because it can become life threatening and it is not really acceptable from the public.
"I will be taking the CCTV up through the trust."
Two front line vehicles were on duty at the ambulance station on the night.
The damaged ambulance has now been repaid and is back in service.
Chorley Police are investigating the incident.
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