National security police said on Friday nine men were arrested on suspicion of unlawful drilling – the first time that section 13 of the Safeguarding National Security Ordinance had been used to make an arrest.

The suspects, aged 20 to 25, allegedly gave and received illegal military training in an industrial unit in San Po Kong.

“The national security department received intelligence that some people had been stockpiling weapons in an industrial building in San Po Kong,” said chief superintendent Steve Li.

“The intelligence also highlighted that inside the flat they offered some military-type training.

"The training involved, according to our intelligence, some firearms handling, use of a tactical knife, compacting skill and radio communication training.”

Officers raided the unit on Thursday evening and arrested six people who were inside, with officers alleging they were conducting firearms and combat training.

They arrested three others in Yau Ma Tei and Tuen Mun later.

Officers also seized air guns, real and fake knives, explosives and a 3D printer.

Li did not rule out further arrests, saying more people could have received similar training before.