Prosecutors said the men intended to lure officers into an ambush by ransacking shops during a pro-democracy rally, before detonating bombs and shooting them.

Ng Chi-hung, a 28-year-old former engineer, was given a total of 23 years and 10 months over the bombing offence and another charge of possessing firearms with the intent to endanger life.

It is the longest sentence handed out yet for a case relating to Hong Kong's huge and at times violent pro-democracy protests, and the first case to invoke the city's anti-terrorism law since its 2002 enactment.

After city authorities tried to fast-track a bill in 2019 allowing for the extradition of Hong Kongers to China, millions took to the streets for protests that morphed into calls for greater political freedoms.

Over the seven months of unrest, smaller sections of hardcore protesters frequently battled police in often violent confrontations that saw more than 10,000 people arrested.

The court heard the men were members of radical groups, one of which was called "Dragon Slayers", which planned the attack along the route of an International Human Rights Day rally in December 2019.

High Court judge Judianna Barnes said Ng was "the mastermind", who "in order to fulfil his own political purposes, aimed to indiscriminately slaughter police officers and subvert the Hong Kong government".

The other six men received shorter sentences, including the alleged leader of the "Dragon Slayers", 26-year-old Wong Chun-keung, who was sentenced to 13.5 years in prison.

David Su, who was recruited as a sniper at the age of 18, was jailed for 12 years.