Police in Hong Kong used tear gas, water cannons and pepper spray to try to disperse anti-government protesters who threw rocks and blocked a key road in the city.
The unrest came at a huge pro-democracy rally, near the local headquarters of China's People's Liberation Army.
Thousands of people, young and old, gathered peacefully at a harbourside park to mark the fifth anniversary of the "Umbrella" pro-democracy movement on Saturday.
Protesters had spent the afternoon rebuilding "Lennon Walls" of anti-government graffiti, some of which were torn down by pro-Beijing activists last weekend.
Meanwhile, opposition activist Joshu Wong announced he would stand in local elections. He was one of the leading voices of the Umbrella Movement.
There were also a smaller number of pro-Beijing protesters making their voices heard ahead of the seventieth anniversary of Communism in China on Tuesday.
The protests were sparked in June by planned legislation that would have allowed the extradition of suspected criminals to mainland China.
It's been withdrawn but the protests have now expanded into a broader pro-democracy movement.