More than 100 primary school children under the age of 12 sat transfixed in the City Hall theatre on Tuesday as a woman wearing a teddy bear headdress reminded them to never disclose state secrets, part of a new campaign by the city's Security Bureau.

Across town, five election candidates vying for legislative seats took part in a government-organised forum where each stuck to their own script without directly challenging their opponents.

The two events reflect how the Chinese finance hub's political landscape has been transformed since Beijing imposed a national security law in 2020, following huge and sometimes violent pro-democracy protests.

Clifton Ko, a film director who shot to fame in the 1980s with irreverent comedies, was tapped by security officials to play to a more serious tune this time.

Ko, who co-produced the interactive drama featuring the teddy bear, told AFP that the 2019 protests were "a challenge to national security".

Now, he said, "we are not just conveying a thematic message or explaining a law, we are healing the wounds we have endured."

The bear mascot told children that their homeland must "remain free from disruption, allowing everyone to live in peace".

The crowd was taught to cross their arms to signal disapproval for bad deeds, such as sharing disinformation online.

Grade three student Elvis Chan, who was selected by his school to speak to reporters after the show, said he liked "Security Bear".

"It's the smartest... It knows a lot about the National Security Law," Chan said.

The drama will head to at least 20 primary schools, adding to national security content already incorporated into the curriculum.

Authorities are also hyping up the Legislative Council election set for December 7, eager to avoid a repeat of the record low turnout seen last time.

Beijing overhauled Hong Kong's electoral system in 2021 to ensure only "patriots" could hold office, and slashed the number of directly elected seats.

Feisty debates hosted by media outlets used to be a fixture in Hong Kong elections, but no such event has been announced this year.

The "Patriots Collaborate for Good Governance" forum on Tuesday was held during office hours and drew many elderly people.

The five candidates all belonged to pro-Beijing parties.

Their campaign staff and volunteers were allowed to chant slogans, but only within a 30-second window allotted by the host.