Demonstrators in Hong Kong urged President Donald Trump to "liberate" the semi autonomous Chinese territory, as they marched to the US Embassy on Sunday to drum up international support for their months-long protest.
However violence later broke out in the business and retail district as police fired tear gas when protesters vandalised subway stations, set fires and blocked traffic.
The march comes a day after attempts to disrupt transport to the city's international airport were thwarted by police.
Hong Kong has been rocked by a summer of unrest kicked off by a proposed law that would allow criminal suspects to be sent to mainland China for a trial.
Many saw the extradition bill as a glaring example of the Chinese territory's eroding autonomy since the former British colony was returned to China in 1997.
The government promised last week to withdraw the bill - an early demand of protesters - but that has failed to appease the demonstrators, who have widened their demands to include other issues, such as greater democracy.
Demonstrators flooded a park in central Hong Kong, chanting "Resist Beijing, Liberate Hong Kong" and "Stand with Hong Kong, fight for freedom."
Many of them, clad in black shirts and wearing masks, waved American flags and carried posters that read "President Trump, please liberate Hong Kong" as they marched to the U.S. Consulate nearby.
The unrest has become the biggest challenge to Beijing’s rule since Hong Kong’s return from Britain.
Beijing and the entirely state-controlled media have portrayed the protests as an effort by criminals to split the territory from China, backed by hostile foreigners.
Protesters on Sunday urged Washington to pass a bill, known as the Hong Kong Democratic and Human Rights Act, to support their cause.
The bill proposes sanctions against Hong Kong and Chinese officials found to suppress democracy and human rights in the city, and could also affect Hong Kong's preferential trade status with the US.
However, President Donald Trump has indicated that the US would stay out of a matter he considers to be between Hong Kong and China.
He has said he believes the US trade war with China is making Beijing tread carefully.
Just before the rally ended, violence broke out after riot police detained several people and chased a crowd out of the nearby Central subway station.
Angry protesters smashed glass windows and sprayed graffiti at the station's exits, and burned cardboard boxes and other debris to start a fire at one of the exits.
The government said protesters also blocked traffic at a major thoroughfare near City Hall in the area, paralyzing traffic.
In the type of cat-and-mouse battle that has characterized the summer-long protests, riot police pursued groups of protesters down streets, but they kept regrouping.
Police fired multiple rounds of tear gas in the Causeway Bay shopping area after protesters heckled them and refused to leave.
The US State Department said in a travel advisory on Friday that Beijing has undertaken a propaganda campaign “falsely accusing the United States of fomenting unrest in Hong Kong”.
It said US citizens and embassy staff have been the target of the propaganda and urged them to exercise increased caution.