The Hong Kong activist Joshua Wong has been sentenced to 10 years in prison after earlier pleading guilty to “foreign collusion”, his second conviction under a national security law critics say has been used to silence political opposition in the city.

Wong, who rose to prominence as the teenage face of Hong Kong’s 2014 pro-democracy demonstrations, submitted his guilty plea in September. He had been accused of working with the exiled Hong Kong activist Nathan Law to urge foreign powers to impose sanctions, blockades or other hostile measures against China.

In his ruling on Thursday, the high ​court judge William Tam ‌described Wong’s actions as “grave in nature”.

He said Wong had visited the US to seek foreign interference before the national security law’s introduction in 2020, and continued to share posts on social media by Law calling for sanctions after it was enacted.

Wong’s role was to “supply his underground support” and “arouse the attention of foreign countries to bolster the cause”, the judge…