Several protesters have been arrested while trying to run from a Hong Kong university campus surrounded by police.
A group of around 100 people tried to leave Polytechnic University, but were met with tear gas and rubber bullets.
It is the third time protesters have tried to leave, following a violent and fiery overnight stand-off with police.
In the past week, Polytechnic University has turned into a battleground as the long-running Hong Kong protests become more violent.
Meanwhile – as protests were raging – a Hong Kong court ruled the government’s anti-mask law unconstitutional.
In October, the government invoked a colonial-era emergency law to make wearing masks illegal – but protesters largely defied the ban.
At around 13:45 local time, around 100 protesters tried to run from the campus but were met by police trying to arrest them.
Images showed protesters pinned down by officers amid clouds of tear gas.
Police officers had earlier said protesters could leave the campus via another exit – the Cheong Wan Road South Bridge – but urged them to drop their weapons and remove their gas masks.
But pro-democracy lawmaker Ted Hui – who is on the campus – said the bridge had “been sealed off”, and it was not possible to leave this way.
Mr Hui earlier said there were up to 1,000 protesters on the site.
Protesters also attempted to leave the campus just after sunrise, but were met by tear gas and rubber bullets.
Police said the gas was fired because “a large group of masked rioters…suddenly charged at cordons”.
Earlier, at around 05:30, protesters threw petrol bombs and lit fires when police tried to enter the campus.
According to Mr Hui, many on campus are injured, and staff from the Red Cross were later seen entering the site.
The acting president of PolyU’s student union Ken Woo said fresh water was available, but food supplies were running low.
Earlier, the head of the university, Professor Jin-Guang Teng, released a video statement to protesters, saying he had arranged a deal with the police.
If protesters left peacefully, he said he would “personally accompany” them to the police station where he would “ensure your case is fairly processed”.
PolyU has been occupied by protesters for several days. On Sunday night, police warned protesters they had until 22:00 local time (14:00 GMT) to leave the campus.
Some left, but others stayed, throwing petrol bombs and bricks at police and even firing arrows from bows.
Police warned they could use live ammunition if the attacks continued.
The BBC’s Gabriel Gatehouse, who was at the scene, said there was a game of “cat and mouse” with police.
“The police fire tear gas and the water cannon advances, squirting noxious blue liquid,” he said.
“The protesters, crouching behind umbrellas, respond with petrol bombs and rocks fired from improvised catapults. The police vehicles retreat. The net result is zero.”
A statement from the university on Sunday night said it had been “severely and extensively vandalised”.
In interviews with media, a number of them identified themselves as current students.
But it is unclear now how many of those left on the PolyU campus are, in fact, university students.
The protesters earlier appealed for university alumni and others sympathetic to the cause to join them as reinforcements.
Campuses remained relatively free of violence during the Hong Kong protests. But earlier last week, the Chinese University of Hong Kong became a battleground.
Police said protesters threw petrol bombs on a major road near the university in an effort to stop traffic. Officers attempted to reclaim the road, leading to major clashes.