A building superintendent was among three men arrested in connection with a marijuana grow-operation spanning nearly two dozen apartment units in a single Toronto highrise, police said.

Officers first entered the 13-storey North York building on Jane Street, north of Sheppard Avenue West, around 10 a.m. Thursday to execute five search warrants, but then found a number of other apartments also housing marijuana plants.

More than 6,000 marijuana plants were seized from 22 apartments. The estimated street value of the seized plants is more than $6 million, with an additional 15 kilograms of dried marijuana valued at $45,000.

At a news conference Friday, police showed a video of what they are calling a "sophisticated" operation that produced high quality marijuana likely headed to the United States.

Coverings to conceal smell

The video showed holes in the walls, high wattage lights and screens covering windows in an effort to conceal the operation.

Coverings had been placed on mail slots and oven vents were left on at all times to reduce the smell of the operation. Unlike many operations, it was soil-based rather than hydroponic.

"You can see the mould and the moisture and the buildup on the walls," said Toronto police Sgt. Dave Malcolm. "You can see the spores floating around inside the apartment."

Officers donned protective gear and masks when entering the apartments to keep from breathing in mould spores or bringing them away from the building on their clothes.

Inside, officers found pots of plants and floors strewn with toxic fertilizers. They said the operations were a fire hazard.

Fire at building earlier in year

Toronto police refused to comment on what sparked the investigation.

Earlier this year, officers were alerted to a grow-op in one of the apartments in the building after a fire at the building, but police said Friday they never detected additional operations.

Police made a special point of thanking Toronto Hydro Corporation and the city's Municipal Standards and Licensing Division for their help in the investigation.

Grow-ops in apartment buildings can be difficult for police to detect because some buildings have a single hydro meter. That makes it less likely spikes in electricity consumption will be noticed.

Building had power outages in summer, tenant says

Shocked residents watched as officers wheeled out bags of marijuana and equipment throughout the day.

Michael Gates, who recently moved into the building, said he never noticed anything out of the ordinary.

He recalls a few power outages during the summer that were quickly fixed by the landlord and remembers catching a whiff of marijuana from time to time.

"I guess with any building nowadays you're going to smell stuff like weed … so we smelled that a few times, but I just passed it off as someone having fun in the stairway," said Gates. "I didn't realize it was any bigger than that."

He's now considering moving out of the building, worried a grow-op may not be the only criminal activity going on there.

Meanwhile, city health and fire officials will be checking the building Friday for air quality, fire hazards and mould.

All three Toronto men arrested in connection with the grow-operation appeared in a courtroom at Old City Hall on Friday morning.

Daniel Wallace, 47, of Toronto faced charges of conspiracy to commit an indictable offence. Police described him as the superintendent of the building.

Thirty-five-year-old Tat Thang Nguyen was charged with conspiracy to commit an indictable offence, five counts of producing marijuana and five counts of possession for the purpose of trafficking.

Dinh Pham, 46, is also charged with conspiracy to commit an indictable offence, producing marijuana and possession for the purpose of trafficking.