A cannabis factory was found in the grounds of a mental hospital, police have confirmed.
Detectives unexpectedly found 30 illegal plants in a disused ward in Whitchurch Hospital, Cardiff, while searching for a missing person.
It is believed the dealer or gang responsible had also hooked up powerful ultraviolet lights and ventilators powered by the hospital's electricity supply.
A police spokesman said: "South Wales Police can confirm a cannabis factory of around 30 plants was discovered within the grounds of Whitchurch Hospital in Cardiff."
The hidden factory was discovered when police were searching for a missing person on June 30.
Officers entered a former ward in the hospital's main building - which had been boarded up and isolated for decades - before finding the cannabis.
While hospital security guards make regular patrols, it is believed they do not enter any of the boarded up buildings on the site.
Cardiff and Vale University Health Board, which runs the hospital site, said it was doing all it could to help the police with their investigation.
Abigail Harris, the health board's director of planning, said: "We would like to reassure the public the health board's security teams carry out regular patrols of all our sites.
"This has happened in a small corner of a big hospital in an area that was sealed and unused for many, many years. It is a highly unusual and isolated case which is being carefully reviewed with police.
"The health board is doing all we can to support the investigation and find those responsible.
"We would encourage anyone with information about this incident to contact the police."