Some 6,000 people arrested but not charged during the 2019 protests could live normally, Secretary for Justice Paul Lam has stressed, while dismissing suggestions on setting a time limit for prosecution.

In newspaper interviews published on Monday, Lam said individuals under investigation for their acts during the social unrest were not bound by any restrictions, and could exercise their freedoms like anyone else.

The justice chief shot down calls to stop pursuing suspects after a certain period of time, clarifying there's no time limit on prosecution for "serious criminal cases".

Setting a deadline, he added, would be "inconsistent" with the principle of the rule of law.

"Our decision to prosecute is based on existing evidence. But there were instances in the past...where there could be changes in circumstances or the emergence of new evidence in the future that's unknown to us, which might make it necessary to re-examine the prosecution decision," Lam explained.

His views were echoed by security minister Chris Tang, who was asked the same topic in a media interview on Monday.

Dropping prosecution after a certain period of time, he said, was like "making things that are illegal lawful".

"Unless the law stipulates a time limit, we will initiate prosecution when there's evidence," Tang said.

The former police chief denied it was unfair to keep arrested individuals waiting for years.

It would only be wrong, he said, if law enforcement agencies have sufficient evidence but choose not to prosecute swiftly.