The raids, codenamed operation Arrowhorn, were launched on 10 August after the COVID-19 pandemic had seen the number of illegal gambling operations increase in the area.

According to Chief Inspector Tse Tsz-kwan, the gambling dens were set up to “absorb customers and earn quick money” after legal mahjong parlours and game centres were closed to combat the pandemic.

The raid operation lasted for a period of two weeks and saw officers seize 34 arcade machines, 15 mahjong tables and HK$63,000 (US$8128) in cash.

Police found the underground casinos in old residential blocks, commercial industrial buildings and a garage.

The 153 detainees were arrested on various offences, including operating a gambling establishment and gambling unlawfully. In Hong Kong, gambling in an illegal establishment carries a maximum penalty of nine months in Jail and a HK$30,000 fine. Operating such an establishment carries a maximum penalty of seven years in jail and a HK$5m fine.

Police found 17 of the suspects to be non-Chinese residents, some of whom were domestic helpers. Five of the suspects were holders of recognisance forms which prohibit them from taking employment.