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 ahead of 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 said. He described Wong’s actions as part of a “scheme” to collude with foreign governments.

Tam said Wong’s sentence would run concurrently with the remaining term of his previous national security offence.

After the ruling, Law said in a statement: “It’s incredibly sad to see my friend Joshua Wong suffer another sentencing over his peaceful advocacy work for Hong Kong’s democracy. The signal the sentencing sent to the world is that [China] is determined to quash any hopes for freedom and democracy on its soil.”

Amnesty International’s deputy regional director, Sarah Brooks, said: “Today’s sentence is another grim reminder of how Hong Kong’s national security law has become a tool to punish dissent rather than to genuinely protect national security.”

Wong wore a dark blue shirt and thick rimmed spectacles in court, and nodded and bowed as supporters waved. Dozens of people had waited in line outside the court building for the hearing, amid a heavy police presence. A group of international diplomats were also present for the sentencing.

The former student leader is already serving a prison term of four years and eight months, imposed in November 2024, for conspiracy to commit subversion for his role in an unofficial primary election. He has spent nearly six years in detention and had been due to be released in January 2027.

The US consulate in Hong Kong said in a statement that it “strongly condemns” the additional sentence and called for Wong’s immediate release. “Wong has been unjustly imprisoned since December 2020, demonstrating that Beijing will go to extraordinary lengths to silence those who advocate for fundamental freedoms in Hong Kong,” a consular spokesperson said.

Shortly afterwards, China warned against “irresponsible” remarks on Hong Kong’s judicial affairs. “Relevant parties should earnestly respect China’s sovereignty, respect Hong Kong’s legal system, stop making irresponsible remarks regarding the trial of … judicial cases,” the foreign ministry spokesperson, Guo Jiakun, told reporters.

Wong, 30, gained international attention during the 2014 Umbrella protests, which paralysed the city’s financial centre and galvanised a generation of young people. In October 2014, he appeared on the cover of Time magazine under the headline: “The face of protest.”

When protests erupted in 2019 over a proposed extradition bill, Wong was serving a prison sentence for his role in the 2014 demonstrations. He was released at the height of the protests and immediately took to the streets.

The following year, Beijing introduced a sweeping national security law it said was needed to restore stability to the former British colony, but critics say has been used to target political opposition, dissolve civil society groups and silence independent media.

Wong is the only activist in Hong Kong prosecuted twice under the law.