Hundreds of people have stormed Hong Kong's parliament as anger grows over plans to allow extradition to mainland China.
Water cannons and tear gas have been fired at protesters during ugly scenes over the controversial bill.
Dramatic video shows tear gas being fired at crowds after bricks were hurled at riot police.
Masked demonstrators have been in a stand-off with authorities for days, with thousands attempting to block access to government buildings.
Hong Kong's Legislative Council (LegCo) is widely expected to allow the move on June 20.
Tens of thousands of protesters had gathered peacefully in the Chinese-ruled city before tempers flared, some charging police with umbrellas.
Police warned them back, saying: "We will use force."
The protesters, most of them young people dressed in black, had erected barricades as they prepared to hunker down for an extended occupation of the area, in scenes reminiscent of pro-democracy "Occupy" protests that gridlocked the former British colony in 2014.
The yellow umbrella was the trademark of those demonstrations.
Protesters rallied in and around Lung Wo Road, a main east-west artery near the offices of embattled Hong Kong Chief Executive Carrie Lam, as hundreds of armed riot police, some with plastic shields, warned them to stop advancing.
"Didn't we say at the end of the Umbrella movement we would be back?" pro-democracy lawmaker Claudia Mo said, referring to the name often used for the "Occupy" demonstrations, whose trademark was the yellow umbrella.
"Now we are back!" she said as supporters echoed her words.