Hands
The biggest difference is how a win is defined. Hong Kong players win with four sets and a pair (or special hands) meeting a faan minimum. American players win only with a hand printed on the current card — patterns of pungs, kongs, quints, pairs and singles with set values.
Equipment and jokers
American sets add eight jokers and need racks; Hong Kong sets have no jokers. In American play flowers stay in the hand as usable tiles; in Hong Kong play they are set aside for bonuses.
Calling and the Charleston
American play starts with the Charleston and allows calls only for groups of three or more (or for Mah Jongg). Hong Kong play has no Charleston and allows chows from the left and pungs and kongs from anyone.
Feel
Hong Kong mahjong is fast and fluid, focused on efficient set-building. American Mah Jongg is a matching puzzle against the card, with jokers, exposures and defense against visible hands. Many players enjoy both.
