A Hong Kong martial arts coach accused of running an armed separatist movement with his assistant has been charged with sedition, police said Tuesday, after a raid that seized weapons including crossbows and machetes.

Police allege the coach, 59, and a 62-year-old female assistant -- both of whom face weapons charges -- set up a martial arts training hall to "incite hatred" against the government and organise "an armed force for Hong Kong independence".

"The arrested persons were deeply affected by misinformation and became self-radicalised... Now they are spreading the misinformation to others," senior superintendent Steve Li told a press conference.

Hong Kong's colonial-era sedition law, which lay unused for decades, has reemerged in the past year as a key tool in the ongoing crackdown on dissent that followed 2019's massive democracy protests.

Authorities said they are also considering more serious charges for the duo under the sweeping national security law Beijing imposed on the city in response to the at-times violent demonstrations.

The male suspect was charged with one count of sedition, while both suspects faced charges related to the possession of weapons and firearms without a license, police confirmed Tuesday afternoon.

The suspects -- arrested Sunday in the city's Tsim Sha Shui district -- are accused of posting anti-government messages including calls to topple China's communist regime and for a "shadow government and self-defence force" to be established.

Hong Kong police display weapons seized during a raid on a Hong Kong martial arts training facility
Hong Kong police display weapons seized during a raid on a Hong Kong martial arts training facility HONG KONG POLICE FORCE via AFP / Handout

"With this vicious cycle, we are very worried those radicalised will go one step further and commit terrorist attacks," Li said.

The arrests came after Hong Kong's National Security Department -- which enforces the law -- sent an undercover officer to the martial arts studio, where the two suspects were teaching "combat tai chi".

Police said they found unlawful weapons including an airgun, eight crossbows, 30 steel-tipped arrows and a collection of blades. Airguns exceeding a certain level of power are considered firearms under Hong Kong law.

The suspects also allegedly urged people to resist anti-coronavirus policies, opposing the government's contact-tracing app and vaccination drives, police said.

Sedition carries a maximum penalty of two years in prison.

Hong Kong authorities have increasingly applied the label of "sedition" to speech that challenges official policies on the coronavirus.

Last month, singer Tommy Yuen and two others were arrested over social media posts that urged people to defy Covid-19 restrictions.