Officers from the Anti-Drug Department, working with Phnom Penh police, stormed the Cambodia Sky Cambodia nightclub on the artificial island and detained 257 people for questioning over alleged drug offenses, the Phnom Penh Post reported.
Among them were 62 Cambodians, including club staff, cleaners, and chefs, and 195 Chinese and Vietnamese citizens.
Police seized at least five kilograms of assorted narcotics, drug paraphernalia, and a large number of mobile phones. All suspects were taken to a National Police detention center for questioning and urine tests.
Those found with drugs or implicated in trafficking will face prosecution, said Lieutenant General Khoeng Sarath, head of the Anti-Drug Department, according to the Khmer Times.
He added that investigators had monitored the venue for about a month before launching the raid.
Koh Pich, or "Diamond Island," sits at the confluence of the Bassac and Mekong rivers and has grown into a major entertainment and commercial hub in Phnom Penh. A day before the raid, authorities carried out 10 separate anti-drug operations nationwide, arresting 26 people and seizing more than one kilogram of crystal meth.