Fifty customers were locked inside a rat-infested fake clothing store in Manchester 's Counterfeit Street.
They had no means of escape, with some trapped on the first floor at the location on Great Dulcie Street.
On Sunday police were on patrol in the area and saw a man acting strangely as he tried to shut the premise's shutters, the Manchester Evening News reports.
The man, who was in his 60s, was detained, and police managed to open the doors as a group of customers ran out.
Inside, in an additional three rooms on the second and third floor, more customers were found.
When the man spotted the police, the people inside had been locked in there against their will.
A search of the property found excessive amounts of rat urine and faeces across the building, including on the shelves and all over clothing, underwear and make up that was being sold at the store.
In the basement, officers could not see the floor for boxes and bags full of items which would be sold after being stored in unsanitary conditions.
Greater Manchester Police said: "Officers discovered incredibly dangerous infrastructure and signs of exploitative labour, including an underground homemade air conditioning system the staff had made by drilling holes into the pipes on the ceiling."
An estimated 20 tonnes of replica clothing, shoes, perfumes and make up have been seized from the building.
Manchester City Council Trading Standards and Greater Manchester Fire and Rescue Service were involved in the operation.
Detective Superintendent Neil Blackwood said: “The state of this building was disgusting and so structurally unsafe. My team found members of the public trapped on the top floor with no means of escape.
“This isn’t the first time we’ve had to rescue members of the public from these buildings, but I urge people to think twice about entering these shops.
"With our presence increasing, the shop owners are becoming increasingly nervous and quick to lock the doors, no matter who is inside.
“By entering these shops, not only are you putting yourself in danger and at risk of the volatile staff, but you’re funding serious organised crime which is having a devastating impact on the local community.
"These people do not care for your welfare; they’re simply trying to make some quick cash.”
David Minto, Protection Manager at Greater Manchester Fire and Rescue Service, said: “We’re working in partnership with Greater Manchester Police on Operation Vulcan and our Fire Safety Officers are conducting fire safety inspections within the premises they’re raiding.
"Our fire safety inspectors attended this property and deemed it so unsafe, a prohibition notice has been served.
"Together we’re working hard to rid Greater Manchester of this illegal and dangerous activity that blights communities.”
The seizure was carried out by officers from GMP's Operation Vulcan which has waged a relentless war on criminals operating in the Cheetham Hill and Strangeways area since October.
An estimated 33 organised crime groups from across the UK are known to be linked to a large cluster of counterfeit goods shops on Bury New Road.
