Officials on Tuesday said witnesses overseas will not be allowed to testify via live video link in national security cases, under a provision in the Article 23 legislation being scrutinised.

Currently, Hong Kong courts decide whether people from abroad could give evidence through video livestream in criminal proceedings, subject to appropriate conditions.

Acting law officer of the Department of Justice, Daphne Siu, said that will not be the case for national security cases in future.

"If the witness gives evidence outside Hong Kong, we don't have effective measures to ensure that he or she isn't testifying under interference or coercion," she told lawmakers in a bills committee meeting scrutinising draft national security legislation.

"If that's the case, the course of justice would be perverted and there would be a risk to national security."

Meanwhile, security minister Chris Tang said authorities will consider devising subsidiary legislation or a code of practice for Article 23 after New People's Party lawmaker Regina Ip made such a suggestion.

"In order to be forward looking, I think it's well worth looking into whether we should have subsidiary legislation to allow the law to quickly adapt to future developments in society and achieve the useful effect that we hope for," he said.