Police in Hong Kong have used water cannon and tear gas against protesters throwing petrol bombs and bricks near government offices in the city.
The violence broke out after thousands of pro-democracy demonstrators marched in defiance of a police ban.
Earlier hundreds rallied outside the British Consulate, demanding the UK press China to maintain freedoms guaranteed during the 1997 handover.
Months of unrest were sparked by a now-scrapped extradition bill.
It would have made it possible for people in Hong Kong to be extradited to mainland China, where critics say they could face human rights abuses.
Earlier this month the bill was finally withdrawn – but protesters continue to call for full democracy and an investigation into allegations of police brutality.
What is happening in the clashes?
Reports say some protesters threw bricks at police outside China’s People’s Liberation Army base, which is near to the Hong Kong parliament and government offices.
They also set fire to a banner proclaiming the 70th anniversary of the founding of the People’s Republic of China, Reuters news agency reported.
One water cannon truck caught fire after being hit by a petrol bomb, Reuters said.
One of the water cannon was firing blue jets of water, which have been used elsewhere in the world to identify protesters later.
For the second week running, some marchers carried the US Stars and Stripes flag and called for President Donald Trump to “liberate” Hong Kong.
Why was there a protest at the UK consulate?
While Hong Kong is part of China, the “one country two systems” arrangement gives it a high degree of autonomy and protects rights such as freedom of assembly and freedom of speech.
But the protesters outside the British Consulate shouted “One country, two systems is dead” and “Free Hong Kong”.
“It was promised that Hong Kong people would enjoy basic human rights and such protection,” one demonstrator told the BBC.
“We believe that the UK government has the legal rights and moral obligation to protect Hong Kong people,” he added.
China insists it is committed to the arrangement.