The paramedics, who were not on duty at the time they were seen at the tip, are believed to have used the ambulance to carry green waste to the tip in St Austell.
The South Western Ambulance Service NHS Trust says the crew was on a 30 minute break at the time of the alleged incident.
The trust’s official statement said: “Thankfully and most importantly, this situation was in no way detrimental to patient care because the crew were not booked on duty.
“The trust takes matters of this nature very seriously however and would like to make an assurance that the matter will be investigated thoroughly.”
Sam Bond