The number of voters could drop for the first time in six years after nearly a quarter of a million voters put themselves at risk of disqualification for failing to verify their addresses.
It means that only 3.45 million Hongkongers will be eligible to vote in the Legislative Council elections in September.
A spokesman for the Registration and Electoral Office (REO) said yesterday its unprecedented clampdown on vote-rigging activities had left 230,000 voters on an omission list because they had so far ignored requests to validate their address, despite being given six weeks to reply.
Another 25,000 non-respondents were believed to have died.
However, a two-month voter registration campaign which ended last month enrolled 147,000 new voters, which means the total number of voters would fall by 108,000 - 3 per cent fewer than last year.
Voters on the omission list still have until the end of this month to respond before being disqualified.
Raymond Tam Chi-yuen, minister for constitutional and mainland affairs, said the size of the omission list did not surprise him. He said previous years had seen about 100,000 disqualifications and added: 'This year we have done more checking by random sampling and visits to housing estates.'