Two Hong Kong pro-democracy protesters have crawled through 500 metres of sewers to try to escape the former colony’s besieged university campus.

The men were arrested when they emerged from a manhole on a road outside the city centre PolyU campus that has been the focus of protest activity for almost a week.

The pair were detained, along with four others who had lowered ropes to help them out from the drainage system, police said.

Of the hundreds who have been holed up in the Hong Kong Polytechnic University for days, only a small group remains on the campus. They are refusing to leave because they will face arrest if they do so, and police have set up a cordon around the area to prevent anyone from escaping.

Since the police siege of the campus began on Sunday, officers have arrested 700 people who left to surrender. A further 300 minors have been allowed to go home but might still face prosecution, Chief Superintendent Ricky Ho said.

Others made successful and daring escapes – shimmying down ropes and jumping on waiting motorbikes – or making a run for it during the night.

An injured protester is helped out of the university campus. Photo: Getty

Chief Superintendent Ho said officers saw four people remove the manhole cover and lower a rope into the drain to help two others climb out. All were arrested for offences including “taking part in a riot” and “assisting offenders”, he said.

It is thought fewer than 100 remain on the besieged campus. About two dozen were scrounging through supplies in the cafeteria looking for food on Thursday morning.

Hong Kong schools have reopened after a six-day shutdown but students and commuters faced transport disruptions.

Workers have also started cleaning up debris blocking a major road tunnel, but it was unclear when it would reopen.

Officials warned protesters not to disrupt elections scheduled for the weekend.

One protester, who spoke on condition of anonymity, remained adamant, saying: “I think if you go out and surrender, it just shows you agree with what the police and that government are doing or have given up the fight.”

Hong Kong PolyU today pic.twitter.com/7ioGtIc63m

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There were scattered incidents of protesters stopping trains by opening emergency doors and blocking traffic on Thursday, but on a much smaller scale than last week.

Television footage showed long queues at some stations because of train delays. A few stations remained shut because of damage from earlier protests.

A group of protesters, joined by pupils in uniform, blocked traffic at one junction. Others in the area argued with them, removing some of the metal barriers that protesters carried into the street.

Even as the latest violence wound down, a fundamental divide suggested the protests in the former British colony are far from over.

Office workers joined protesters at lunchtime in the central business district to show support for the movement, as they have every day since last week.

Hong Kong’s protests began in June over an extradition bill that would have allowed suspects to be sent to China to face trial. The bill has been withdrawn, but protesters now demand fully democratic elections and an independent investigation into police actions in suppressing the protests.

Protesters also have called on the government not to cancel Sunday’s neighbourhood council elections. Chief Secretary Matthew Cheung, Hong Kong’s No.2 official, said officials were “extremely keen” to hold the vote.

“But much depends on the co-operation of violent protesters. It takes two to tango,” he said, adding that blocking roads and disrupting traffic will make it hard for people to vote.

The Hong Kong government joined China in condemning passage of legislation by the US Senate that mandated sanctions on Chinese and Hong Kong officials who committed human rights abuses, and required an annual review of Hong Kong’s favourable trade status with the US.

The Hong Kong Open golf tournament has been postponed because of the unrest, the latest in a string of disrupted public events.

-with AAP