Police yesterday discovered a thriving marijuana farm inside a sixth-floor flat in To Kwa Wan.
A total of 400 pots of marijuana were confiscated in the 300-square-foot flat in Kowloon City Road, but no arrests were made.
Police did not say how they came to know about the illicit operation.
A preliminary investigation suggested that the plants were cultivated for the local market. The mature plants were about one meter tall.
The flat was found to be equipped with sunlamp lighting and a sprinkler system. It had a well- designed ventilation system fitted with an odor filter to mask the smell of the marijuana.
The windows were covered with opaque plastic to prevent anyone seeing inside.
Police could not say if a syndicate is believed to be involved.
"We don't yet know if the marijuana has reached the public. The case is still under further investigation," said Kowloon City assistant district commander Yeung Chi-choi.
Yeung said there is no evidence of a trend toward indoor marijuana growing.
Ivy Chan, who runs an air-conditioning engineering company on the ground floor of the building , said she had no idea an illegal marijuana farm existed on the premises.
"I am so shocked to know there was an unlawful plantation upstairs," she said. "People coming in and out of the building are old neighbors and no suspicious strangers have been spotted in the past few months."
Police want to speak to anyone who may have witnessed suspicious activity in the street, including cars coming and going from the premises. In January last year, 600 pots of marijuana valued at HK$2.4 million were seized from a remote Yuen Long village house of 600 square feet.
Two men, aged 36 and 41, both surnamed So, were arrested during the raid at Shui Chiu San Tsuen.
In October 2007, the city's biggest marijuana nursery was raided.
Some 1,500 plants were seized, along with equipment, in a Kwai Chung industrial building unit measuring about 3,000 square feet.
It is illegal to cultivate marijuana in Hong Kong.
Those found guilty can face a maximum penalty of 15 years in jail and a fine of HK$1 million under the Dangerous Drugs Ordinance.