Police in Canada have charged dozens of people and seized millions in assets after discovering that a sprawling mansion north of Toronto was thriving as a underground gambling den while legal casinos were shuttered due to the coronavirus lockdown.

York region police announced 74 charges on Wednesday connected to a months-long investigation into illegal gambling operations in Ontario. As well as making 29 arrests, police seized more than $10m in assets, firearms, cash and high-end liquor.

“This is organized crime truly exploiting and demonstrating their money, their positions and opulence thinking somehow that they are above the law,” York police’s deputy chief, Brian Bigras, told reporters.

The main target of the raid was a 20,000 sq ft mansion, sitting on a two-acre property in an affluent suburb of north York. The upstairs rooms of the house were used as a bed and breakfast, but police say the basement had been transformed into a luxury underground casino and spa.

When 92 tactical officers stormed the property on 23 July, they found dozens of gamblers at mahjong tables and slot machines, a full cash bar and a kitchen serving food including banned items such as shark fin.

Patrons were not following Covid-19 protocols, including wearing masks and maintaining physical distancing.

The owner of the operation, Wei Wei, faces a number of charges, including selling liquor without a permit, illegally possessing a firearm and operating a gambling establishment.

His wife, Xiang Yue Chen, was charged with keeping possession of proceeds of crime and selling liquor. The couple’s two children were also charged with various crimes.

Along with more than $1m worth of alcohol, police seized a number of firearms, including an AR-15 rifle with a 30-round magazine along with a handgun found in the bedroom of the mansion’s owner.

Police were forced to call off a previous attempted raid after aerial surveillance of the property showed that children were on the property. Police believe the family was hosting a private event and had armed guards posted throughout the area.

Police also believe the mansion was the site of a potential sex-trafficking operation and said the investigation is ongoing.

“The money moving through these underground casinos leads to huge profits for criminals that fund other ventures such as prostitution and drug trafficking,” the York region police chief, Jim MacSween, said in statement. “This illegal high-stakes gambling also leads to gun violence, armed robberies, kidnappings, extortion and other serious violent offences within our community.”