The Independent Commission Against Corruption (ICAC) on Sunday said three people have been arrested for allegedly inciting others to cast invalid ballots or refrain from voting during the District Council elections, violating the Elections (Corrupt and Illegal Conduct) Ordinance.

They include a couple both aged 41. The woman works for the Department of Health as a clerical officer and the man is unemployed.

The ICAC said they allegedly left a comment on a social media post which encouraged others to put three or more ticks on their ballot papers.

The graft-buster said officers had seized the duo's mobile phones after searching their residence.

The pair have been detained for investigation, the ICAC said, adding that further law enforcement actions are possible.

"In accordance with established procedures, upon completion of an investigation, the findings will be forwarded to the Department of Justice for legal advice on whether there is sufficient evidence to instigate a prosecution," the ICAC said in a statement.

Separately, the body arrested a 51-year-old for allegedly sharing a social media post by Lee Man-ho, a former district councillor who's no longer in Hong Kong, that incited others not to vote, while urging people to cast invalid votes by writing their names and identity card numbers on ballot papers.

"As Lee had already left Hong Kong, the ICAC will apply to the court for a warrant for his arrest," the ICAC said.

"The [elections ordinance] has extraterritorial effect and applies to all conduct concerning an election, be it engaged in, within Hong Kong or elsewhere."