Winning Mark Six will be harder but jackpots could balloon to as much as $100 million under changes designed to stabilise the fluctuating turnover of the game.
Punters will also have a chance to win a new seventh prize of $20 if they pick three winning numbers.
From July 4, seven winning balls will be drawn from 49 instead of 47 in each game, reducing the probability of winning first prize from one in 10.8 million to one in 14 million. Punters need to get the first six numbers correct to win the jackpot.
However, the revamp introduced by the Hong Kong Lotteries Board also brought some good news for punters, including increasing the amount of the fourth, fifth and sixth prizes to $4,800, $320 and $160 - from $4,500, $300 and $150.
The $38 million cap on the top prize, imposed in 1992 to prevent syndicates from wagering on all combinations of numbers to ensure winning the top prize, is to be removed.
Also, a seventh prize of $20 will be paid to entries with any three of the six drawn numbers selected. Each ticket costs a minimum of $20 when bought from computerised machines.
Statistics expert Paul Yip Siu-fai, a senior lecturer at the University of Hong Kong, said the changes would make the already difficult feat of winning Mark Six even harder.
