Secretary for Security Chris Tang said on Tuesday government plans to ban two groups accused of subverting state power from operating in Hong Kong are necessary to safeguard national security.

The Security Bureau issued written notices to "Hong Kong Parliament" and the "Hong Kong Democratic Independence Union" on Monday to allow them to make representations as the security chief looks to exercise his powers under Hong Kong's homegrown national security law to ban their operations in the SAR.

Tang said the two groups undermined the country's constitution and the body of power of the SAR, having carefully considered all relevant information.

"In the event of the two organisations being formally declared prohibited, it would be unlawful for anyone to act as a member of these organisations, attempt to incite others to join them, participate in their activities, or provide assistance," he said

Nineteen members of "Hong Kong Parliament" had fled and been listed as absconders, Tang said, and one member was earlier sentenced to one year in prison for subversion while four members of the "Hong Kong Democratic Independence Union" are facing trials over subversion.

Tang said another member of the "Hong Kong Democratic Independence Union" is now wanted by the ICAC over allegations of calling on people not to vote or cast blank ballots during next month's Legislative Council election.

So far, 29 people had been arrested in connection with the election, mostly for alleged vandalism, he said, adding that some people remain determined to undermine the electoral process.

He stressed authorities must and would strictly enforce the law against anyone attempting to influence elections through any means.