The unit was stolen in the Penylan area of Cardiff

The crew who work for the patient transport service section of St John Wales were helping their patient in Cardiff when the thief took the device.

The medics said they noticed someone's arm coming through the door window and rip out the device before the culprit made off on a bicycle.

South Wales Police are investigating.

The incident happened in the Penylan area of Cardiff as the ambulance crew - Craig Israel and Chris Mayhew - was transporting an elderly patient from the University Hospital of Wales to his home.

Craig Israel (left) and Chris Mayhew were in disbelief

Chris Mayhew said: "We just couldn't believe it. We were helping this gentlemen who was unsteady on his feet and we just saw this arm come through the window and grab the satnav.

"The patient wasn't affected in anyway. We are just disappointed that someone would do such a thing." St John Wales' patient transport service ambulances are all equipped with the satellite navigation equipment in order for staff to be able to find patients homes quickly.

Dorien Williams, the manager for the service said: "It is our role to help people who are often unable to care for themselves.

"Our professional staff are out there safely transporting hundreds of patients from hospital to their homes every week.

"We feel that it is such a shame that someone has taken advantage of a vulnerable situation and stolen from one of our much needed ambulances."

Anyone with any information about the theft is asked to contact Cardiff Central Police Station on 02920 222 111.