HONG KONG • A Hong Kong cleaner at a mahjong parlour has been sentenced to eight months in jail for letting in two men who switched the mahjong tiles.

The mahjong tiles were changed to those which had markings that reveal the players' hands, reported Hong Kong media.

Wong Kin Ming, 29, now a driver, pleaded guilty last month to one count of attempting to cheat at gambling.

He was sentenced by a Hong Kong court on Tuesday, reported South China Morning Post.

The case involved six mahjong sets placed on three tables at the mahjong parlour in in Yau Ma Tei.

The markings on the backs of the tampered tiles were invisible to the naked eye but when viewed with a special pair of glasses, they would help reveal the symbols and Chinese characters of the tiles, the Kowloon City Court heard.

But none of the tampered mahjong tiles made it to an actual game because the manager of the mahjong parlour noticed that they were of a different colour.

The manager looked at the CCTV footage and saw the cleaner opening the door for the two men on Jan 16.

Upon arrest, Wong said a stranger named "Ah Fai" had promised to pay him HK$3,000 (S$530) a day to open the door to his accomplices to switch the tiles.

He also told police that "Ah Fai" planned for someone to play in the mahjong parlour so they could cheat other players.

Wong's lawyer revealed in mitigation that he never received the reward, according to the Post.

Separately, last November, a 55-year-old cleaner and three Chinese nationals were jailed for tampering with automatic mahjong tables at another parlour in Yau Ma Tei, reported Apple Daily.