Detective Sergeant Jason von Tunk, of the Portland police crime investigation unit, said 360 mostly mature cannabis plants were located at a Grassmere property on Monday morning.

"We executed a warrant at 6.30am Monday at the Grassmere property. A large mechanics shed had been divided into eight grow rooms," he said.

"It was a large hydroponic set-up involving watering and fertiliser systems, an electrical bypass and electrical transformers and lights.

"The majority of the plants were mature and ready to harvest."

So far in the south-west police Operation Highrise there have been seven grow houses and one drying operation located in Portland, Hamilton, Warrnambool, Horsham and now Grassmere.

"Grassmere was an outstanding result in this ongoing operation to combat the cultivation and supply of cannabis," Detective Sergeant von Tunk said.

"It's an ongoing operation. Follow up inquiries are taking place in relation to Grassmere.

"What we have already located indicates there are more cannabis grow houses out there in the community."

A number of Vietnamese nationals have been charged in relation to the crop grow houses and are in the process of going through the court system.

The detective requested that anyone who saw unusual activity, such as people coming and going at odd times or bright lights coming on at regular times, contact their local police station or Crime Stoppers on 1800 333 000.

Tuesday: The 350 cannabis plants seized from a Grassmere property on Monday morning, with a potential street value of more than $500,000, are expected to be transported to a police facility and destroyed.

Detective Senior Constable Michael Vaughan, of the Portland police crime investigation unit, said it was the largest cannabis grow house bust in the current Operation Highrise.

That operation has uncovered seven cannabis grow houses in the south-west and one Hamilton drying operation.

The crop houses have been located in Warrnambool, Portland, Hamilton and Horsham.

"We got 307 plants in one crop house at Hamilton, so this was significantly more," he said.

"Powercor workers turned up about 11am Monday to totally disconnect the electricity bypass which had been put in place and make sure everything was completely safe.

"Two botanists from the Victoria Police forensic unit arrived at 12.30pm and it took nine police members and the two botanists until 5pm to load a truck with all the plants."

Detective Senior Constable Vaughan said a large mechanics shed had been converted into eight rooms to house the hydroponics set-up.

"It was a very large hydroponics operation complete with water and fertiliser systems, electric transformers and timers," he said.

"The mechanics pits had been filled with leftover soil and rubbish. Inquiries are continuing and it's an active investigation," he said.

It's understood the property was sold by a Grassmere district family about 18 months ago to people who claimed to be from Geelong.

A number of Vietnamese nationals have been charged in relation to other crop houses located across the south-west.

Neighbours reported seeing people at the Grassmere property a number of times cutting the lawn, but no vehicles were sighted.

Police executed a warrant at the Grassmere Road property at 6.30am Monday and found the grow house, complete with 350 cannabis plants, ranging from seedlings to mature plants ready to harvest.

It takes the total number of cannabis plants seized in Operation Highrise to almost 2000.

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