Police in riot gear move through a cloud of smoke as they detain a protester today at the Hong Kong Polytechnic University in Hong Kong. Hong Kong police fought off protesters with tear gas and batons today as they tried to break through a police cordon that is trapping hundreds of them on a university campus. (AP Photo/Ng Han Guan)

HONG KONG (AP) — As night fell on Hong Kong, police tightened their siege of a university campus where hundreds of protesters were trapped in the latest dramatic episode in months of protests against growing Chinese control over the semi-autonomous city.

The Asian financial center’s work week began today with multiple protests that disrupted traffic, while schools remained closed because of safety concerns stemming from the demonstrations, which began in June but have become increasingly violent in recent weeks.

The pitched battle for control of the campus of Hong Kong Polytechnic University has been the center of the most recent developments. For days, protesters have fortified the campus to keep out the police. Now cornered by police determined to arrest them, they desperately tried to get out but faced a cordon of officers armed with tear gas and water cannons.

Officers repelled one escape attempt this morning with tear gas, driving hundreds of protesters back onto the campus. Later, huge crowds of supporters advanced on foot toward the police from outside the cordon to try to disrupt the police operation.

Some protesters descended by ropes from a footbridge to a road below, where they were met by motorbike riders helping them flee as police fired teargas at them. It was unclear whether they got away safely.

Senior government officials said they were trying to de-escalate the situation and urged the protesters to peacefully leave the campus and cooperate with police — advice that seemed certain to lead to arrests and therefore strengthened the protesters’ resolve to resist.

Local council elections scheduled for Sunday are now at risk of being delayed because of the unrest, said Patrick Nip, Hong Kong’s secretary for constitutional affairs.

“The situation in the past weekend has obviously reduced the chance of holding the election as scheduled. And I am very anxious about this,” Nip said, adding that the government “won’t take this step unless absolutely necessary.”

Riot officers broke in one entrance before dawn as fires raged inside and outside the school, but they didn’t appear to get very far. Fiery explosions could be seen as protesters responded with gasoline bombs. Police, who have warned that everyone in the area could be charged with rioting, reportedly made a handful of arrests.

The give-and-take has played out repeatedly during the city’s months of anti-government unrest. The protesters want to avoid arrest. The police want to pick up as many as they can.

“These rioters, they are also criminals. They have to face the consequences of their acts,” said Cheuk Hau-yip, the commander of Kowloon West district, where Polytechnic is located.

“Other than coming out to surrender, I don’t see, at the moment, there’s any viable option for them,” he said.

Cheuk said police have the ability and resolve to end the standoff peacefully so protesters should not “try their luck.”

While both sides dug in at the campus, protest supporters rallied in nearby districts across Kowloon as they attempted to get close to the police cordon to disrupt the law enforcement operation and help those trapped inside. But they were met at multiple locations by riot police firing tear gas, turning the busy streets teeming with apartment blocks into a battle zone.

Protesters won on a legal front today when the high court struck down a mask ban imposed by the government last month. The court said it did not consider anti-mask laws unconstitutional in general, but in this case, the law infringed on fundamental rights further than was reasonably necessary.

Many protesters wear masks to shield their identities from surveillance cameras that could be used to arrest and prosecute them. The ban has been widely ignored, and police have charged protesters with wearing masks.

The protests started peacefully in early June, sparked by proposed legislation that would have allowed criminal suspects to be extradited to the mainland. But by the time the bill was withdrawn, the protests had hardened and broadened into a resistance movement against the territory’s government and Beijing.

Activists see the extradition bill as an example of Hong Kong’s eroding autonomy under Beijing’s rule since the 1997 handover from colonial power Britain.

The head of a nationalistic Chinese newspaper said Hong Kong police should use snipers to fire live ammunition at violent protesters.

“If the rioters are killed, the police should not have to bear legal responsibility,” Global Times editor Hu Xijin wrote on his Weibo social media account.

Anti-government protesters barricaded themselves inside Polytechnic last week. Police surrounded the area Sunday night and began moving in after issuing an ultimatum for people to leave the area. The crowd wore raincoats and carried umbrellas to shield themselves from police water cannons.

At daybreak, protesters remained in control of most of the campus. In one outdoor area, some demonstrators made gasoline bombs while others dozed while wearing gas masks. Two walked about with bows and quivers of arrows, while many stared at their smartphones.

“We are exhausted because we were up since 5 a.m. yesterday,” said a protester who gave only his first name, Matthew. “We are desperate because our supplies are running low.”