The Department of Justice then started contempt of court proceedings against those arrested. Eleven of them, including Wong, who is currently serving a six-month jail sentence for another Occupy-related protest, admitted to the charge in July. But nine, including jailed political activist Raphael Wong Ho-ming, contested the charge and were put on trial.

During the trial, they insisted they had either failed to hear the announcements asking them to leave the site or were in the process of leaving when they were arrested.

But the judge disagreed. In a 44-page written judgment, he noted that the clearance operation had been publicised and it was “highly unlikely that any citizen of Hong Kong would misapprehend the situation”. Those who remained at the site knew precisely what they were doing, he said, and this caused “interference with the due administration of justice”.

In particular, the judge did not accept claims from defendant Mak Ying-sheung that she was an intern reporter covering the protest for online news portal Independent Media. The judge pointed out that he had seen video footage of her chanting alongside other protesters, putting an “extra burden” on officers doing their duty at the scene.

“This case is not about the right or wrong of the Occupy movement,” Justice Chan said.

With the verdict,Wong could face an extension of current his six-month sentence, which already bars him from running in Legislative Council elections for five years.

Wong turned 21 on Friday, and will be transferred from a correctional facility to an adult jail. He said “thank you” to his supporters who chanted “happy birthday” outside the courtroom before the session began. They sang a birthday song for him when the hearing ended.

Wong and two other student leaders of the Occupy campaign, Alex Chow Yong-kang and Nathan Law Kwun-chung, were packed off to prison in August. The trio were convicted of storming into the forecourt of the government headquarters two days before the Occupy protests shifted into full gear on September 28, 2014.

They were originally spared jail by a lower court, but prosecutors hauled them back to an appeal court, arguing that a lenient sentence would send the wrong message to the public. Separately, 13 other activists were also given jail terms for storming the Legco complex in June 2014 to oppose the government development plans for the northeast New Territories.

Accusations of political motivation in activist jailings ‘totally unfounded’, Hong Kong’s chief executive Carrie Lam says

Student activist Lester Shum, who is among the group of 20, on Friday said he was prepared to go to jail but expected a short imprisonment.

Watch: Activists Chan Po-ying, Chiu Chi-sum and Lester Shum protest against the “political persecution” of Occupy protesters

Meanwhile, local group Socialist Action announced that lawmakers and activists around the world had taken part in its “Stop Repression in Hong Kong” campaign, to mark the first anniversary of the disqualification of two pro-independence lawmakers and express concerns over the jailing of 16 young political activists, including Joshua Wong, in August.

On Thursday, they staged demonstrations outside the Chinese embassies or the Hong Kong government’s trade offices in 22 cities.

The 11 who pleaded guilty in the contempt case:

Chau Wan-ying

Chu Wai-lun

Cheung Kai-yin

Ma Po-kwan

Lester Shum

Cheung Kai-hong

Choi Tat-shing

Jason Szeto Tse-long

Wong Lai-wan

Joshua Wong Chi-fung

Yeung Ho-wah

The nine who denied guilt but were ultimately convicted:

Chu Pui-yan

Kwok Yeung-yuk

Chiu Chi-sum

Chan Po-ying

Kwan Siu-wang

Hung Cheuk-lun

Fung Kai-hei

Mak Ying-sheung

Raphael Wong Ho-ming