Thieves dug a 100ft tunnel under a building to steal a cash machine.
Police believe the gang may have spent more than six months digging the passage however reports suggest they only got away with around £6,000 from Blockbuster in the Fallowfield shopping precinct in Manchester.
The theft occurred sometime between 2 January and 3 January, with the tunnel running from an embankment at the rear of the shop, under a car park and below the shop's foundations.
The tunnel, which was only 4ft tall, surfaced directly underneath the cash machine, with the criminals forced to cut through 15 inches of concrete.
"In all my years of service, I have never seen anything quite as elaborate as this," said Detective Sergeant Ian Shore, from Longsight CID.
"These people had obviously spent a long time plotting this crime and I doubt they would have been able to keep their plans secret for all that time, without telling others about their scheme.
"They must also have spent a lot of time in the area over the past few months, which people may have noticed.
"The financial detriment to the victim could have been a lot worse, and the offenders did not get away with as much money as I believe they may have originally hoped. The machine had limited funds available."
He added: "I would ask that anyone who may have noticed anything unusual around this Blockbuster store, or who may have seen or heard anything they think might help us with our investigation, to get in touch."
Anyone with information is asked to call police on 0161 856 4245 or contact the independent charity Crimestoppers anonymously on 0800 555 111.
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