Security Secretary Chris Tang on Monday said it is reasonable to extend the maximum detention period for national security suspects who haven't been charged, from the current 48 hours to 16 days.

Lawmakers scrutinising planned security legislation under Article 23 of the Basic Law asked Tang whether the proposed two weeks will be long enough.

"We have to strike a balance between police investigation and the protection of human rights. Based on Hong Kong's actual circumstances, we've probed national security cases before and we believe [an extra] 14 days is reasonable for conducting a preliminary investigation," he said.

Justice Secretary Paul Lam noted that the courts will get to decide if the prolonged detention is warranted, adding that authorities would not restrict people's freedom of movement unless it was necessary to do so.

Information given to the courts during applications for extended detention need not be shared with those being held. Lam brushed aside lawmakers' concerns that this will be unfair to those under arrest.

"Even though the arrested persons may not have access to all the confidential information the police are keeping, they can still say through their lawyers that they're law-abiding citizens, and that they'll fully cooperate with the investigation after being released," he said.

"They'll still have the chance to express themselves freely."