Hong Kong police have laid siege to a university where hundreds of anti-government protesters are bunkered down with petrol bombs and other homemade weapons, amid fears of a bloody crackdown.
Officers fired volleys of tear gas and rubber bullets to force back dozens of activists who tried to escape the besieged campus of Polytechnic University on Monday.
The action followed a night of mayhem in which major roads and a police armoured van were set alight and an officer was shot with an arrow.
Dozens of protesters were arrested near the university, public broadcaster RTHK reported, while in the nearby commercial area of Nathan Road activists stopped traffic and forced shopping malls and stores to shut.
"We've been trapped here for too long. We need all Hong Kongers to know we need help," said Dan, a 19-year-old protester on the campus, as he burst into tears.
"I don't know how much longer we can go on like this. We may need international help."
Thirty eight people were injured overnight on Sunday, the city's Hospital Authority said. Some suffered burns from chemicals in the jets fired from police water cannons.
"Remember you have life in your hands. Why do you need to push us to death?" one person shouted from a campus rooftop as protesters in gas masks and clutching umbrellas looked for ways to escape.
Live video showed others with their hands tied behind their backs sitting cross-legged on a road as riot police stood guard in one of the busiest commercial and tourist districts.
Police said they fired three live rounds when "rioters" attacked two officers attempting to arrest a woman. No one was injured and she escaped.
Police had earlier warned they were ready to use live bullets if "rioters" continued to used lethal weapons, amid a dramatic escalation of the unrest that has plunged the Asian financial hub into chaos for almost six months.
Demonstrators angry at what they see as Chinese meddling in the former British colony have said they are responding to excessive use of force.
The United States condemned the "unjustified use of force" and called on Beijing to protect Hong Kong's freedom.
"We condemn the unjustified use of force and urge all sides to refrain from violence and engage in constructive dialogue," said a Trump administration official.
Chinese soldiers in a base close to the university were seen on Sunday monitoring developments with binoculars, some dressed in riot gear.
The city's Cross Harbour Tunnel link to the Kowloon peninsula remained shuttered and protesters torched a footbridge that crosses the highway, authorities said.
Some train services and many roads across the Kowloon peninsula remained closed.
All schools were shut.
Meanwhile, thousands of residents and protesters flocked to districts around the university to try to penetrate the riot-police lines and rescue the trapped students.