Hong Kong police have stormed into a university campus held by protesters after an all-night stand-off.
Fiery explosions could be seen inside as riot officers entered before dawn on Monday.
Police had fired repeated barrages of tear gas and water cannon at protesters outside the campus since before midnight.
Anti-government protesters had barricaded themselves inside Hong Kong Polytechnic University for days, fighting back with petrol bombs and bows and arrows.
Police threatened early on Monday morning to use live ammunition on protestors after an officer was skewered by an arrow on Sunday - marking a severe escalation after more than half a year of protest.
The continuing conflict around the semi-autonomous state's universities has seen protesters set a bridge on fire to keep police - armed with tear gas and water cannon - from advancing on their campus stronghold.
Police said the arrow struck a media liaison officer in the calf on Sunday and he was taken to a hospital. Photos on the department’s Facebook page show the arrow sticking out of the back of the officer’s leg.
Now officers have said they will consider the use of live bullets - ammunition which has only been deployed fleetingly throughout the protest, including one incident when an off-duty officer fired on a crowd, striking a boy in the leg.
In Monday's statement, police warned people who they described as rioters to stop using lethal weapons to attack officers and to halt other acts of violence, saying office would respond with force and possibly live bullets if necessary.
As riot police moved in on the university from all sides, some protesters retreated inside Hong Kong Polytechnic University while others set fires on bridges leading to it.
A huge blaze burned along much of a long footbridge that connects a train station to the campus over the approach to the Cross Harbour Tunnel, a major road under Hong Kong’s port that has been blocked by the protesters for days.
Protesters are trying to keep the pressure on Hong Kong leaders, who have rejected most of their demands.
The protests were sparked by proposed legislation that would have allowed the extradition of criminal suspects to the mainland.
Activists saw it as an erosion of Hong Kong’s autonomy under the “one country, two systems” formula implemented in 1997, when the UK returned the territory to China.
The bill has been withdrawn but the protests have expanded into a wider resistance movement against what is perceived as the growing control of Hong Kong by communist China, along with calls for full democracy for the territory.
Police and protesters faced off all day on Sunday after a pitched battle the previous night in which the two sides exchanged tear gas and petrol bombs that left fires blazing in the street.
A large group of people arrived in the morning to try to clean up the road but were warned away by protesters.
Riot police shot several volleys of tear gas at the protesters, who sheltered behind a wall of umbrellas and threw petrol bombs into nearby bushes and trees, setting them on fire.
The protesters held their ground for most of the day, as water cannon trucks drove over bricks and nails strewn by protesters to spray them at close range – some with water dyed blue to help police identify protesters afterwards.
Protesters began retreating into the university near sunset, fearing they would be trapped as police fired tear gas volleys and approached from other directions.
The protesters have barricaded the entrances to the campus and set up narrow access control points.
They are the holdouts from larger groups that occupied several major campuses for much of last week.
Another group threw bricks in the street to block a main thoroughfare in the Mongkok district, as police fired tear gas to try to disperse them.
The disruption to traffic on Nathan Road may have been an attempt to distract police during the standoff at the polytechnic.
Opposition politicians criticised the Chinese military for joining a cleanup to remove debris from streets near Hong Kong Baptist University on Saturday.
Dozens of Chinese troops, dressed in black shorts and olive drab T-shirts, ran out in loose formation and picked up paving stones, rocks and other obstacles that had cluttered the street.
The military is allowed to help maintain public order but only at the request of the Hong Kong government.
The government said it had not requested the military’s assistance, describing it as a voluntary community activity.
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