Some 50 people were held against their will on Great Dulcie Street, in an area of Manchester known for its fake shops.
A man in his 60s was detained – and later released pending further investigations – after he was seen behaving suspiciously while trying to close the shutters on the building.
Police had to use an angle grinder to get into the shop and when they did a group of people came flooding out.
Once inside, they found more people crammed into three other rooms on the second and third floor.
The building was littered with rat urine and faeces – including on shelves and over clothing, underwear and make up that was being sold at the illegal outfit.
‘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.’
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.
The fire service deemed the property unsafe and a prohibition notice was served.
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.