Wiltshire Police are appealing for witnesses following the theft of a set of ambulance ignition keys in Calne.
The incident took place at about 2am yesterday outside the Talbot Inn, Calne.
The ambulance service were called to the pub just before 1.30am on Sunday as a 24-year-old man had suffered a cut arm which was bleeding.
But while treating a patient, an unknown person accessed a rapid response vehicle and drove it 20 metres down the road before running off with the keys.
An ambulance later took the man to the Great Western Hospital in Swindon.
PC Mel Neal said: "This was a mindless act which could have resulted in an extremely serious incident for the patient being treated.
"The ambulance wasn't in use for the rest of the night which could have put other people's lives at risk too.
"We still haven't located the keys to the vehicle but someone will know who was involved in this incident and I would urge them to come forward."
Anyone with information is asked to contact PC Neal at Chippenham Police on 101 or Crimestoppers on 0800 555 111 where information can be left anonymously.
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