Hong Kong police and pro-democracy protesters clashed in the early hours of Monday in some of the most violent skirmishes seen in recent weeks.
Police baton-charged and pepper-sprayed thousands of demonstrators who had been trying to encircle government buildings.
Two student groups heading the campaign for free elections for the territory’s next leader in 2017 have called on their supporters to escalate their action after two months of stalemate.
The movement has threatened to become the biggest challenge to China’s Communist Party since its 1989 crackdown on pro-democracy protests in Tiananmen Square in Beijing.
Meanwhile there has been a rise in tension between the UK and China over Hong Kong. A group of British MPs who were due to visit as part of an inquiry into relations between the UK and its former colony have been refused entry.