Pro-democracy activists Joshua Wong, Agnes Chow and Ivan Lam were jailed by West Kowloon Magistracy on Wednesday for their roles in an anti-government protest that saw police officers trapped inside their headquarters in Wan Chai for hours.
Wong received 13.5 months behind bars, Chow 10 months and Lam 7 months, with their jail terms reduced in light of their guilty pleas.
But the magistrate said she had used a higher starting point for sentencing Wong because he had taken a "leadership role" in the protest.
Before being escorted out of court, the activist shouted to his supporters: "I know the road ahead is tough, but I will hang in there."
"Add oil!" the crowd shouted back.
Chow, meanwhile, cried upon hearing her punishment.
Her defence announced they planned to appeal, but Chow was denied bail and walked limply out of court.
Thousands of people had laid siege to the building in Wan Chai on June 21 last year, demanding the withdrawal of the government's extradition bill and that police stop describing protests earlier in the movement as "riots".
The crowd blocked the building's entrances, with some protesters vandalising walls and smashing surveillance cameras, but there were no serious clashes with the police.
Wong, 24, pleaded guilty to organising the assembly and inciting others to join. Chow, 23, also admitted inciting people to join the demonstration as well as taking part herself, while Lam, 26, pleaded guilty to the incitement charge.
Lawyers for the three former leaders of the now-disbanded Demosisto group had called for lenient sentences, urging magistrate Wong Sze-lai to take into account the trio's young ages, the fact that Chow had a clear record, and that they hadn't taken part in any violence during the protest.
But the magistrate said the incitement action was premeditated and intended to paralyse road traffic, adding that the protest was large in size and had posed a potential danger to others.
She said the protest had led to a wastage of police resources as the force had to deploy additional manpower to set up a cordon around its own headquarters, and the siege had hindered police work and made it impossible for officers to follow up on dozens of calls for help.
Joshua Wong’s series of actions were targeted at the police and aimed at challenging their authority, the magistrate added.
She said to protect public interests and people’s life and property, she believed the sentences had to have a deterrent effect and immediate imprisonment was the only appropriate option.
After the hearing, a large crowd of the trio’s supporters, including prominent activists Chu Hoi-dick and Grandma Wong, filled the lobby outside the courtroom and exchanged hugs and words of comfort with one another. A few also burst into tears.
A post on Joshua Wong's Twitter account after the hearing said: "It’s not the end of the fight. Ahead of us is another challenging battleground. We’re now joining the battle in prison along with many brave protestors, less visible yet essential in the fight for democracy and freedom for HK".
"The tenacity of HKers continues to give us strength in our sufferings. Please, take your positions, give support to each other," it added, with the post accompanied by the hashtag "#Save12HKyouths", which refers to the group of young Hongkongers detained in Shenzhen.
Joshua Wong and Lam have been jailed in the past for convictions relating to their activism, but this is the first time Chow has been given a prison sentence. In August, she was also arrested under the national security law but was not charged with any offence.