Protesters claimed anti-democracy agitators from the city's triad mobs were being arrested only to be released back into the crowds again.
"The police have been co-operating with gangsters," said David Chan, a 22-year-old student. "We have witnessed the police letting go of the gangsters. That's why the peaceful protesters are so angry, we have no trust in them any more."
Pro-democracy protesters have taken to Hong Kong's streets during the past week to demand the right to nominate who can run as their next leader in 2017 elections. Beijing insists only candidates it has approved will be able to stand.
Student leaders said they would meet the Government if certain conditions were met, having scrapped planned negotiations the previous day over anger at police actions in earlier clashes.
"Even after all these incidents, it shows that the more they suppress us, the more we will fight," the student leader, Joshua Wong, told the Admiralty gathering. The crowd chanted for democracy and roared the unofficial anthem of the movement by the band Beyond.
Watch: Hong Kong protesters threaten occupation
Many also voiced concern about what would come next. Hong Kong's chief executive, Leung Chun Ying, who has refused demands to step down, said in a televised address it was urgent that all entrances to government headquarters were clear today so staff could work and that roads were unblocked so schools could reopen.
He said if the conflict between pro-democracy and anti-Occupy Central groups continued, it would be "very likely to keep getting out of hand" and urged citizens to keep calm. He added that the Occupy movement had seriously affected people's lives, incomes and public services.
The former Democratic Party legislator Law Chi Kwong urged the public not to go to Admiralty and warned that if they did they should be prepared for attempts to disperse them. He told the South China Morning Post the Government might act "no later than tomorrow, or even earlier".
The heads of the universities committee appealed to students to leave all Occupy rallying areas and put safety first, but many said the violence had motivated them to attend.
"It's so outrageous about the tear gas first and then the violence in Mong Kok ... We believe if we don't come out we will not be able to voice our opinions as freely," said Keith Wong, 45.
Yanki Wong said she feared protest numbers would soon dwindle because people would have to return to work after the weekend.
- Observer, AFP
