Petrol bombs were thrown at Hong Kong police and water cannon fired in response as an evening rally descended into violence in the city.
Thousands of people gathered to mark the fifth anniversary of the Umbrella Movement in 2014: that petered out after 79 days.
But one of the students who led the movement at the time told Sky News the pro-democracy demonstrators are determined that's not going to happen again.
Joshua Wong, 22, told us that the fresh swell of pro-democracy feeling in Hong Kong is different and much stronger than 2014.
Mr Wong, who has announced he will stand for the city's district council elections in mid-November, said: "People are willing to pay the price and make the sacrifice which has allowed our movement to go forward."
The rally had to end early after concerns were voiced about safety. A man waving a Chinese flag was set upon by protesters and badly beaten.
Hundreds of protesters threw rocks at police and lobbed them at windows of the central government offices.
They smashed up the bus stops and advertising hoardings nearby.
Police fired 'sponge' bullets and rounds of teargas, and water cannon was deployed, including using the controversial blue dye.
The dye is difficult to remove and causes a burning sensation. Its use has raised alarm among human rights' monitors.
Many of the protesters were openly telling each other to save themselves for the 70th anniversary of Communist Party rule in China on 1 October.
Many of Hong Kong's National Day celebrations have been scaled down for fear of violence and the city is bracing itself for days of unrest.