The day of protest precedes the United Nations summit on how to rein in the worst effects of climate change.
A march was not permitted by police, but protesters took to the streets anyway, building a wall out of barricades and setting it on fire.
Protesters have taken to the semiautonomous Chinese territory’s streets for more than two months.
The central government in Beijing ominously characterized the current protest movement as something approaching "terrorism."
Demonstrations began early last month in opposition to an extradition bill that has since been suspended, but the movement has become a push for full democracy.
Demonstrators took to the streets again on Sunday, chanting "Free Hong Kong" and demanding the resignation of the city's leader.
Officers manage to separate tense groups in dueling rallies.
Police say some "milkshakes" hurled in skirmishes included quick-drying cement.
As massive demonstrations continued over a reviled extradition bill, Hong Kong's top official issued an apology on Sunday.
Over 100 people were reportedly killed in the capital and across Sudan in a sweeping crackdown last week.
Pro-democracy protesters said Wednesday that dozens of bodies of people slain by Sudanese security forces were pulled from the Nile River in Khartoum.
Omar al-Bashir has been arrested in the wake of escalating protests against his 30-year rule.
A reporter and several clergy members were among those detained.
President Emmanuel Macron broke his silence to tweet his appreciation for the police overnight, but pressure mounted on him to propose new solutions to calm the anger dividing France.
Prized Paris monuments and normally bustling shopping meccas locked down and tens of thousands of police took position around France.
The president has vowed that those responsible for the violence and the damages will pay for their actions
Angry over rising gas taxes and government elitism, protesters have been demonstrating for more than a week on the Champs-Elysees.
Women continue to protest the confirmation of Supreme Court Justice Brett Kavanaugh. Right-wing media belittles them.