Chief Executive John Lee said on Monday that he has requested election officials to set up a task force to investigate the cause of an electronic poll register system failure during the District Council polls, with findings expected in three months.

The glitch led to authorities extending voting hours by one and a half hours, and polling stations switching to printed copies of the voter register to issue ballot papers.

Speaking to reporters at a polling station, Lee said he's highly concerned about the incident.

"One of the key tasks for the District Council elections is to ensure that voting and ballot-counting are done efficiently. The system failure that's occurred has resulted in a disparity with our original expectations," Lee said.

"I hope the investigation can go all out to find out the root cause of the issue, to ensure that we can seriously prevent such risks, and that similar incidents will not happen in the future."

The task force – to be led by Electoral Affairs Commission member Bernard Man – will include staff from the Office of the Government Chief Information Officer and the Registration and Electoral Office, as well as police officers from the cyber security and technology crime bureau.

Asked if he's concerned there would be challenges against the voting arrangement, Lee said the most important thing is to have fair and just measures in place after an emergency.

The SAR leader added that the elections had been successful, and that people's participation, the level of organisation and the quality of elected district councillors should not be ignored because of a system failure.