After two weeks of relative calm, the major rally showed that the pro-democracy campaign has not lost support and that hardcore protesters will continue to clash with police.
"You can see Hong Kongers won't easily give up their right to demonstrate... today's turnout is more than I expected," said Daniel Yeung, an unemployed protester.
"You can see that as long as people keep coming out in large numbers we are safe and can keep fighting," he said.
Hong Kong has been battered by months of often massive and violent protests over concerns that Beijing is tightening its grip on the city, the worst political crisis since Britain handed the city back to China in 1997.
Protesters threw petrol bombs at the Tsim Sha Tsui police station on Kowloon peninsula after police inside fired volleys of tear gas to disperse demonstrators on the street.
Some erected fiery barriers on Nathan Road, a major retail strip in the Kowloon district, as riot police, shields in front, marched toward them, while others fired tear gas.
Police used several water cannon trucks to disperse protesters, spraying jets of blue dye into the crowds and sending hundreds fleeing. Police have used the dye to identify protesters.
It was the heaviest use of water cannons by police and many people hit with the water developed coughs, suggesting an irritant may be mixed with the water.
As riot police advanced protesters fell back to their next barricade, unlike past rallies when they stood and clashed with police, throwing petrol bombs and bricks.