HONG KONG: Hong Kong activist Edward Leung, 30, who first used one of the most popular protest chants of the 2019 pro-democracy demonstrations and the first slogan to be declared illegal under a national security law, was released from prison on Wednesday.

Leung first used "Liberate Hong Kong! Revolution of our times" as a campaign slogan for a 2016 legislative election he was later banned from running in, due to his past advocacy for independence from China.

Such advocacy is now a crime under the controversial security law imposed by Beijing in 2020 that carries a sentence of up to life in prison. The first person arrested under the law drove a motorcycle carrying a black flag with the slogan into several policemen.

A court ruled last year the slogan was "capable of inciting secession" and convicted former waiter Tong Ying-kit, 24, for inciting secession and terrorism. About 160 others have since been arrested under the security law.

Leung left Shek Pik Prison, a maximum security institution on Lantau Island, where the international airport is located, at about 3.00 a.m. He did not speak to media.

"Separated for four years, I want to cherish the valuable time to reunite with family and back to a normal life with them. Sincerely thankful to everyone, care and love," Leung said in a Facebook post.

The Correctional Services Department told Reuters that "taking into consideration the wish and safety of the person in custody, (it) has taken corresponding measures to arrange for the person in custody concerned to be released from Shek Pik Prison in the small hours".

Leung was in prison during both the 2019 anti-government protests and the subsequent crackdown under the national security law.

He was jailed in 2018 for his role in an overnight protest in 2016 that turned violent, injuring about 130 people, mostly police, when masked activists threw bricks and burned trash cans to vent anger at what they saw as China’s encroachment on the former British colony’s culture and autonomy.

His six-year sentence for rioting and assaulting police, following the "Fishball revolution," sparked by protests against police action into unlicensed food stalls, was reduced by a third for good behaviour, local media said.

Leung was a leader of Hong Kong Indigenous, a now defunct political group that organised anti-China protests and advocated “localism”, promoting a local Hong Kong identity instead of a Chinese one.

Fellow group members Ray Wong and Alan Li were also charged with rioting in the 2016 protest. The pair later skipped bail and were granted asylum in Germany in May 2018.