One protester climbing down with a guide string as he tries to find an escape route

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HONG KONG - Arms covered in cling film and torches in hand as they drop into the sewers, clusters of pro-democracy protesters still inside a Hong Kong campus are plotting increasingly ingenious - and desperate - ways to escape a police siege.

Protesters have removed metal manholes, some making exploratory forays into the fetid tunnels, following rumours of successful exfiltrations from a campus ringed for three days by baton-wielding police determined to arrest them.

Pockets of protesters, some with thick bandages wrapped around their knees in anticipation of a long crawl to freedom.

AFP reporters saw one group on their stomachs practising crawling. Another group hugged each other in consolation after apparently agreeing not to take the route down into the unknown.

"The people outside can't help us," a protester told local media as he prepared to descend into a sewer. "So what can we do?"

One protester, gas mask on and cling film around his arms, carried a torch as he descended with his backpack down into the subterranean gloom.

So far, the daring escape bids have been matched by their danger. Late on Monday, dozens of protesters in civilian clothes slid down several metres of rope onto a flyover, where a cavalcade of motorbikes conducted a smash and grab rescue mission.

Police said 37 of the escapees and motorcyclists were later arrested - but many others are thought to have got away.

About 100 protesters remained in the Hong Kong Polytechnic University, which has been surrounded by police, after more than two days of clashes. Some 280 injured were taken to hospitals yesterday, the Hospital Authority said.

Police have arrested about 1,100 people in the past day.

Hong Kong leader Carrie Lam said yesterday she hoped a stand-off between police and a group of pro-democracy protesters at a university could be resolved and she had told police to handle it humanely.

In what many will see as an illustration of Beijing's tightening grip, China's legislature questioned the legality of a Monday Hong Kong court ruling that a ban on face masks worn by protesters was unlawful.

The National People's Congress said Hong Kong courts had no power to rule on the constitutionality of city legislation.

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Mrs Lam also did not rule out more violence as she urged peace.

"If the protesters are coming out in a peaceful manner... then there is no situation when that sort of violence would happen," she told a press briefing.

However, police would have to take "necessary action" if the situation changed, she said.

One woman said her son was inside the campus with his girlfriend and they would come out but for the fear of facing charges of rioting, which can carry a 10-year sentence.

"I know the young people see there are many unrighteous things in society, they want to do something to change it," said one woman.

"But as parents, we only have one wish. We only want all of them to come home safely."