Several hundred Occupy supporters lit 1,000 candles outside the Lai Chi Kok reception center last night in support of their leaders being held overnight there.
They sang songs penned in the hey days of the Umbrella movement occupation in 2014 to show their support.
Among them were convicted leader Chu Yiu-ming, who was given a suspended sentence, convener of Civil Human Rights Front Jimmy Sham Tsz-kit, former lawmaker "Long Hair" Leung Kwok-hung, and Labour Party veteran Lee Cheuk-yan.
Earlier in the afternoon, pan-democrats issued a joint statement saying they found the sentences saddening.
Camp convener Claudia Mo Man-ching burst into tears as she called prosecution of the nine Occupy leaders "political oppression."
"This regime attempts to use judicial procedures to silence the opposition in Hong Kong," she said, calling it white terror.
The pro-democracy camp, she said, refused to be disheartened, and will continue to stay positive.
"The Umbrella nine's contribution to our democracy movement will be forever remembered and gloriously written in our history," she said.
Mo also promised the camp will try its best to fight against the extradition law amendment, which could lead to the handing over of political activists to Beijing.
Education-sector lawmaker Ip Kin-yeun said the movement was sparked by failure of political reform, which was spearheaded by Carrie Lam Cheng Yuet-ngor when she was serving as chief secretary back in 2014.
He asked Lam to apologize for her failure and its consequences.
The sentencing also sparked concerns from other countries.
The US consulate-general said such prosecutions can stifle the exercise of the basic freedoms guaranteed in the Basic Law. The British consulate-general stressed that freedom of speech and assembly are both guaranteed in the Sino-British Joint Declaration.
"It is important that these, and all other rights and freedoms which are guaranteed under the joint declaration, are fully respected," a spokesman said. "It would be deeply concerning if the outcome for these individuals were to deter the people of Hong Kong from participating in peaceful protest in the future."
Taiwan's Mainland Affairs Council said it "deeply regretted" the ruling, adding it showed one country, two systems has failed.
Beijing, it said, claimed it will safeguard the mechanism, but on the other hand, it oppresses Hong Kong's human rights and autonomy.
The people of Taiwan will not be deceived by the lies, it added.
Foreign ministry spokesman Geng Shuang said in Beijing that issues concerning Hong Kong are the country's internal affair, and that China opposes foreign intervention.