In a video published by the Hong Kong garrison of the PLA on Friday, the garrison said its ground forces had patrolled Stonecutters Bridge in Tsing Yi, as the air force's helicopters hovered above.

The video, lasting one minute and 27 seconds and posted on Weibo, shows soldiers conducting patrols in Hong Kong with military vehicles, helicopters, and ships.

A caption stated that it was a joint drill that was scheduled for the third quarter of this year, and consisted of exercises on patrolling, stop and search as well as sending injured people for treatment.

"[It is to ] examine the defense capability of the Hong Kong garrison."

A part of the drill involved an inspection and arrests conducted aboard a "suspicious vessel." The video stated that two teams of armed soldiers on a speedboat were guided by a helicopter to chase after the vessel intheir mission area.

As part of the exercise, a person attempts to escape and soldiers were able to capture him by pinning him down on the deck.

"We took the [speedboat] to the 'suspicious vessel' and searched 'suspicious items' on it. We also questioned people on the ship and found they were on our arrest list," one of the armed soldiers told mainland media.

"We then apprehended the persons - the whole process was relatively smooth," he added.

The video also shows a helicopter airlifting someone to hospital. They also practiced extinguishing wildfires.

The garrison stated in the video that the whole drill process strictly abided by locallaws and that the SAR government was notified in advance.

The PLAhas been conducting military drills in locations such as Bohai Sea and Yellow Sea from the end of last month to early this month.

Mainland military experts have said they would respond to interference by external forces and "Taiwan independence" forces.

Twelve Hong Kong protesters and activists, including Andy Li Yu-hin, were intercepted last year by Guangdong coastguards while trying to flee to Taiwan on a speedboat.