I looked up the "Laws of Malaysia - Act 289 - Common Gaming Houses Act 1953"
which defines gaming as:
=== QUOTE ===
"gaming" with its grammatical variations and ognate expressions means the playing of any game of chance or of mixed chance and skill for money or money's worth and includes the playing of any game specified in Column I of the First and Second Schedules and the playing or operation of any gaming machine;
=== END ===

Mahjong isn't specifically mentioned in "Column I of the First and Second Schedules" but "Jin Rummy" is which is pretty close. However, I imagine that the exact game played isn't the point, it's that it's any game of chance played in a public place that is bet upon for money (or similar).

There's an interesting thread about it here.

Search that page for "03-02-2006 01:01 PM" to find a really useful post.

Hope that's of help.

Gareth