Detective Senior Sergeant Chris Asenjo said this week's raid at Portland was the sixth cannabis grow house found in the south-west, as well as a drying operation in Hamilton.

There have been three cannabis crop houses found in Portland and other hydroponic systems in Warrnambool, Hamilton and Horsham homes.

The detective said Operation Highrise was part of a ongoing co-ordinated approach aimed at stamping out the production of cannabis.

"Since March this year, we have seized almost 1500 cannabis plants and around 10kg of cannabis head, totalling a street value of more than $2.5 million," he said.

"Any opportunity to disrupt criminal networks moving significant quantities of drugs is a huge win for the community.

"We will continue to target drug-related offenders in Victoria's south-west and won't rest on our laurels because we know there are other people involved in illegal activities out there."

On Tuesday Portland police arrested a 40-year-old Melbourne man who was charged with cultivating a commercial quantity of cannabis after almost 300 cannabis plants were seized at a Must Street address.

The 40-year-old Vietnamese national was remanded in custody and will appear again in the Warrnambool Magistrates Court at a later date.

It is understood he is living in Australia illegally.

There have now been eight people arrested in relation to the cannabis crophouse raids.

Detective Senior Sergeant Asenjo said all eight had been charged with cultivating a commercial quantity of cannabis, as part of a combined 20 charges.

"All persons have been remanded in custody and will appear in the Warrnambool Magistrates Court at later dates," he said.

"Portland and Hamilton police units including the divisional tasking team and criminal investigation units have joined forces to execute these warrants."

The first crop house in the south-west was located in Warrnambool's Sundale Road during October last year, containing about 300 plants ranging from seedlings to mature plants.

Police say it would take about $50,000 to set up hydroponic systems, including timers, lights, transformers and watering and nutrient systems.

Officers are also investigating the possible seizure of the houses involved as being the proceeds of crime.

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