"Every little helps" says the sign at Tesco where a gang spent months digging away at a 50ft (15m) tunnel to help themselves to the shop's cash machine.

Spurning the traditional bank robbers' tools of balaclava and sawn-off shotgun for the shovel and pick, detectives say the complex tunnel structure would have taken serious planning and weeks of laborious digging to carry out the raid in Salford, Greater Manchester.

And police have not ruled out this latest tunnel raid to two others in the area by the raiders dubbed locally as Mole in the Wall gang.

Last Friday morning, staff opened the shop on Liverpool Road in Salford to peer into a hole in the ground where the gang had broken in.

At the other end of the tunnel, 50ft (15m) across wasteland, was where they made their escape - with the ATM's cash boxes containing a "substantial" sum of money.

Police have appealed to the public who may have seen people acting suspiciously and "possibly covered in soil".

Detective Superintendent Mark Toker, from Greater Manchester Police, said: "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 elaborate scheme.

"The offenders must have spent long periods of time in the area over the last few months, which people may have noticed.

"You may have seen people acting suspiciously on Friday night, possibly covered in soil.

"I would ask anyone with any information about the robbery to call us as soon as possible."

At the scene today there was no police tape to mark the spot where the gang began their marathon dig - only a sign at the shop to say the cash machine was not in use.

Nothing unusual had been noticed by locals passing by, several who broke into smiles of sheer admiration for the gang's audacity.

It is the third time a tunnel gang has struck in the Manchester area.

In 2007 a plot to break into a cash machine on a retail park in Fallowfield was only foiled after workmen laying electric cables, stumbled across the 40ft tunnel.

The shaft, which was just 20ft short of its target, had electric lighting and scaffolding support.

And in January 2012 a Blockbuster shop in Levenshulme, was successfully raided after a gang spent up to six months building a 100ft tunnel with lighting and roof supports, from a railway embankment, under a car park and beneath the shop to the cash machine inside.

Anyone with information on the latest Tesco raid, between midnight and 6am last Friday, March 14, is asked to call police on 0161 856 5353 or call Crimestoppers anonymously on 0800 555 111.