Protesters march amid rising tensions in Hong Kong (Lead)
Opposition groups plan further demonstrations on Sunday and a city-wide strike on Monday, the BBC reported.
Two months of demonstrations sparked by a controversial extradition bill show no signs of abating, with both sides hardening their stance.
Although the government has now suspended the bill, which would have allowed extradition to China, demonstrators want the bill to be fully withdrawn.
Their demands have broadened to include calls for more democracy and for Hong Kong's leader Carrie Lam to resign.
Hong Kong -- a former British colony -- is part of China but enjoys unique freedoms not seen on the mainland. Beijing and the Chinese Army have issued stern warnings about the growing unrest.
Protesters gathered in Mong Kok where violent clashes took place during the pro-democracy protests in 2014.
The police had initially denied permission for the gathering but relented after an appeal.
Demonstrators reportedly walked past a designated end point for their march, chanting slogans and calling on people to join the planned strike on Monday.
Some unions and organisations have reportedly already agreed to take part in the action.
Volunteers were seen handing out masks, hard hats, bottled water and pre-paid subway tickets to marchers. Many businesses along the route closed their doors.
A group of demonstrators blocked access to the Cross Harbour Tunnel, causing traffic chaos. Others set up make-shift barricades on shopping streets.
Saturday's march comes after a group of civil servants -- ordered to be politically neutral -- joined the demonstrations in thousands on Friday.
The rally followed the publication of an anonymous letter on Facebook complaining about "extreme oppression" and listing five key demands -- complete withdrawal of the extradition bill; waiving charges against those arrested; end to descriptions of protests as "rioting"; independent inquiry into the unrest; and resuming political reforms.
"I think the government should respond to the demands instead of pushing the police to the frontline as a shield," a government worker said.
Supporters of Hong Kong's police force have also gathered for a rally on Saturday in Victoria Park.