Hong Kong police used tear gas and water cannons on Monday (local time) against protesters who tried to break through cordons and reach a university at the centre of a week-long standoff between demonstrators and law enforcement.
The black-clad protesters hurled petrol bombs as they tried to get to the Hong Kong Polytechnic University, occupied by activists during a week that has seen the most intense violence in five months of anti-government demonstrations.
"We have been trying to rescue them all day," said a young man in a blue T-shirt, cap and spectacles, running down Nathan Road, the Kowloon district's main commercial street. "They are trapped in there."
Later, about a dozen protesters pinned inside the campus escaped on the backs of waiting motorbikes after lowering themselves with rope onto the road.
The size of demonstrations has dwindled in recent weeks, but clashes between protesters and police have escalated sharply since early last week, when police shot a protester, a man was set on fire and the city's financial district was filled with tear gas in the middle of the workday.
On Monday night, protesters under cover of umbrellas huddled along the median strip in Nathan Road, filling bottles with petrol to make crude bombs, a weapon they have used increasingly.
Some residents were trapped at police cordons, and all the shops along a stretch of commercial strip that is usually one of Hong Kong's busiest were shut.
Earlier on Monday, police tightened their cordon around the Polytechnic University, and fired rubber bullets and tear gas to pin back about 100 anti-government protesters armed with petrol bombs and other weapons and stop them from fleeing.
Dozens, choking on the tear gas, tried to leave the campus by breaking through police lines, but were pushed back.
"The police might not storm the campus but it seems like they are trying to catch people as they attempt to run," Democratic lawmaker Hui Chi-fung told Reuters.
"It's not optimistic now. They might all be arrested on campus. Lawmakers and school management are trying to liaise with the police but failed."
Police said officers had been deployed "on the periphery" of the campus for a week, appealing to "rioters" to leave.
"All roads to Poly U are blocked," said a policeman who stopped Reuters reporters at a road block on Monday night. "All are blocked."
Police say 4,491 people, aged from 11 to 83, have been arrested since protests began in June.
Demonstrators are angry at what they see as Chinese meddling in Hong Kong's promised freedoms when the then British colony returned to Chinese rule in 1997. They say they are responding to excessive use of force by police.
China says it is committed to the "one country, two systems" formula granting Hong Kong autonomy. The city's police deny accusations of brutality and say they show restraint.
China's foreign ministry said on Monday no one should underestimate its will to protect its sovereignty.
On Sunday, Chinese soldiers in a base close to the university were seen monitoring developments at the university with binoculars, some dressed in riot gear.
On Saturday, Chinese troops in shorts and T-shirts, some carrying red plastic buckets or brooms, emerged from their barracks in a rare public appearance to help clean up debris.
The unrest poses the gravest popular challenge to Chinese President Xi Jinping since he came to power in 2012. Beijing denies interfering in Hong Kong's affairs and has blamed Western countries for stirring up unrest.
The Hong Kong government invoked a colonial-era emergency law in October banning faced masks commonly used by protesters. The High Court ruled on Monday the ban was unconstitutional and police said they would suspend all such prosecutions.