Hong Kong pro-democracy activists have clashed with police as thousands of people tried to surround the government's headquarters.
Protesters carrying umbrellas, the symbol of their movement, fought police armed with pepper spray and batons at the main protest camp in Admiralty.
The BBC reports it is some of the worst violence since the protests began two months ago.
There are reports of injuries and arrests, while activists are still blocking one of the major roads.
The protesters want Hong Kong people to be allowed to choose their leaders without interference from Beijing.
One of the protesters there is James Bang who told Radio New Zealand's Checkpoint programme that the situation was "utter chaos".
"It's unbelievable scenes in front of me right now. Earlier there were 150 cops now there are 400 of them. They've got their shields up."
"People are throwing things at the police. Tempers are flying all around. Cops are screaming at people and people are shouting back. Chaos has really broken out here in Admiralty. We've never seen chaos like this at the main town before. This is definitely the first time," said Mr Bang.
"Protestors are now running away and retreating. People are being urged to get away, get away because the police are being very violent at the moment. Objects are being thrown at the police officers. Police are hitting the citizens with their batons. It's utter chaos right now."
The Chinese government has said it will allow universal suffrage for the region's elections in 2017 - but will screen candidates in advance.
The protests were stepped up after police began demolishing one of several camps occupied by the activists during two months of demonstrations.
The latest clashes come as China said it would not allow a UK parliamentary committee to enter Hong Kong as part of an inquiry into British relations with its former colony.
The protests began with a rally on Sunday evening, as student leaders told crowds they would escalate their campaign.
Police later charged at the protesters, attempting to beat them back as they poured into a major road near the offices of Chief Executive CY Leung.
Last week more than 100 people - including some key protest leaders - were arrested as a camp in the Mong Kok commercial district - across the harbour from Admiralty - was dismantled.