The boy was arrested for possessing instruments fit for illegal purposes as officers seized a large amount of shields, folding knives, helmets, respirators and filter cartridges at his home.

He has been released on bail while police are actively investigating if anyone is controlling the boy to engage in the trades.

The other two men included a technician and a waiter, both aged 22.

The technician was arrested in Tin Shui Wai for inciting others to do serious bodily harm within intent. Officers also seized two phones, a helmet, a tactical vest, belt and 13 air guns.

As for the waiter, he was arrested for possessing instruments fit for illegal purposes at his home in North Point, where police also found two smartphones, seven helmets, 28 respirators and filter cartridges and six air guns.

They were both remanded in custody.

Police pointed out that there is no evidence that they are plotting crimes targeting the July 1 celebrations next week.

Still, officers said the arrestees may have breached the interim injunction order issued by the High Court in 2019, which prohibits citizens encourage or incite the use of violence on the internet or other media.

The investigation is ongoing and there may be more arrests made, police added.

In a separate case, three people arrested by police -- including a martial arts coach -- for running an armed separatist movement were released on bail on Friday.

The trio aged form 39 to 50 was accused of sedition and police seized "a large number of offensive weapons" including machetes, knives and swords from their residences when making the arrests on Wednesday and Thursday.