Police are investigating 21 complaints in which voters said others used their identities to cast their ballots.
They include two women who arrived at a Sha Tin polling station to find they were recorded as already having voted.
"I am very angry. Why was I deprived of my right to vote?" asked one of them, Yip Man-fei, 40, a secretary who lives in Sha Tin City One.
She complained to the staff, who said she could still vote, but the word "duplicated" would be stamped on her ballot ticket.
Later another woman, 48, who went to the same polling station, was also told someone had voted with her identity. Police said the identity cards of the two victims had not been stolen or lost in recent months.
They added that all the cases would be handed over to the Independent Commission Against Corruption.
