The "mastermind" accused of running a vast, multi-million dollar synthetic drug dealing network spanning the South Island operated out of a small Christchurch dairy, a court heard today.

Fei He, a 48-year-old woman, is accused of being behind a lucrative, illegal "synthetic cannabis' ring from Sockburn Dairy, which she owned and operated on Main South Rd in the western suburbs of Christchurch.

After a police investigation, dubbed Operation Sin from April 2015 to May 2016, He was charged with possessing and supplying synthetic drugs.

Her trial, along with two of her alleged dairy workers Sui Jun Zhou, a 34-year-old real estate agent who police claimed was her armed delivery driver, and 30-year-old chef Xiwen Miao, along with a fourth alleged dealer, Heng Fu, 35, began at Christchurch District Court today.

Fei He had initially sold the highs legally over the counter, the court heard.

But after the drugs, especially "synthetic cannabis" boomed in popularity in 2010, and then a number of synthetic-drug related deaths, the New Zealand Government moved to ban them. It tightened the laws in 2013 and on May 1, 2014, an amendment to the Psychoactive Substances Act 2013 made it illegal to possess or supply psychoactive substance, including synthetic cannabis.

"It was a very lucrative business," Crown prosecutor Karyn South said this afternoon.

"There was a lot of money to be made selling synthetic cannabis and a lot of people wanted to buy it and smoke it."

Sockburn Dairy was raided in May 2016. Photo / Kurt Bayer

After the drugs were made illegal, it's alleged that He continued to sell them.

And when police scrutiny got too hot, she moved to delivering directly to the buyers, the Crown alleges.

Fei He was the "mastermind" of what the Crown called a major distribution network into the South Island, dealing in vast quantities of synthetic cannabis.

"This was her gig," South said.

Zhou was employed to be the delivery driver, the Crown claims.

He spent "all of his days driving around in expensive 4WD vehicles" selling synthetic cannabis, while armed, directly to customers, South said.

Some of the customers were small-time users, the jury was told, but others were dealers who wanted to buy up to half a kilogram at a time.

After a period of surveillance, police swooped on Zhou on May 11, 2016. Online messages found on his phone, led him to an Avonhead property where Miao had allegedly been tipped off that the police were on to them.

When police raided the house, they found it was where all of the psychoactive substances were being produced and bagged up for sale.

Officers searched the house, along with a vehicle and a Blenheim Rd storage unit, and netted 173kg of psychoactive substances, which had a street value of $3m-$4m, the court heard.

Earlier searches of Sockburn Dairy, the Crown say, found synthetics tucked away in a magazine shelf, an ice cream cone box, a light fitting ceiling cavity, and in a sock in a ceiling fan.

When spoken to by police, He claimed they were only herbal products, "relying on traditional Chinese herbal knowledge".

He, Fu, Zhou, and Miao face a variety of charges, including possession of psychoactive substances for sale, selling or supplying a non-approved psychoactive substance, and possession for supply of a non-approved psychoactive substance. There are 25 charges in total. Fu faces just one representative charge.

He, Zhou, and Miao are also charged with money laundering under proceeds of crime legislation, variously accused of shifting money through bank accounts, making loans, and buying Christchurch property and cars.

Zhou admitted three charges before the trial got underway: unlawful possession of a restricted weapon, namely a stun torch, a shotgun, and ammunition on May 11, 2016.

The trial, before Judge Stephen O'Driscoll, is scheduled to last six weeks and involves five Mandarin translators.

The Crown is expected to call up to 50 witnesses during the trial, which continues tomorrow.