Police are surrounding a Hong Kong university campus after a fiery overnight stand-off with hundreds of protesters inside.

Dozens of protesters tried to leave after sunrise but turned back as police fired tear gas and rubber bullets.

The police said tear gas was fired because “a large group of masked rioters…suddenly charged at cordons”.

Earlier, police tried to enter Polytechnic University (PolyU) but were met with petrol bombs and bricks.

The acting president of PolyU’s student union Ken Woo told broadcaster RTHK that at least 500 people remained inside the campus.

He said fresh water was available, but food supplies were running low. Demonstrators have been occupying the site for days, as Hong Kong’s violent protests continue to escalate.

On Monday afternoon, police said protesters could leave the campus via Cheong Wan Road South Bridge – but urged them to drop their weapons and remove their gas masks.

But Mr Woo said some had decided to stay put as they would be “arrested anyway” if they left.

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”.

What is happening at Polytechnic University?

The campus has been occupied by protesters for several days, and a statement from the university on Sunday night said it had been “severely and extensively vandalised”.

Overnight, protesters threw petrol bombs and bricks at police, and even fired arrows from bows.

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.”

When police tried to enter the campus at around 0530 local time, they were met with petrol bombs, which started more fires around the site.

After sunrise, dozens of protesters tried to leave the site – but turned back after being met with tear gas and rubber bullets.

One student told the Reuters news agency: “At first I felt very scared and panicked staying here, because the police said all of us inside the university would be arrested for charging riots and we will be sentenced for 10 years or above.

“But now I feel very peaceful because I believe that everyone inside our university will stay together.”

On Sunday night, police warned they could use live ammunition.

“I hereby warn rioters not to use petrol bombs, arrows, cars or any deadly weapons to attack police officers,” police spokesman Louis Lau said.

“If they continue such dangerous actions, we would have no choice but to use the minimum force necessary, including live rounds, to fire back.”

On Sunday, a member of police staff was hit in the leg with an arrow apparently fired by a protester from a bow.

Who are the protesters left in PolyU?

In interviews with media, a number of them identified themselves as current students.

But it’s 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.

By Sunday evening, PolyU officials said the campus had been “occupied by activists”. They also urged all staff and students to evacuate.

Democratic Party politician Hui Chi-fung, who is currently on campus, told a radio station on Monday that many of the remaining protesters appeared to be young teens and secondary school students.