“Our main goal is to restore the safety of the campus and reopen it as soon as possible,” he said.

After the university appealed on Monday for an end to the blockade, police assembled a “safety team” to enter the campus in Hung Hom and persuade the remaining protesters to leave.

But the force held back from moving in after PolyU preferred to send in its own search teams to look for the last remaining protesters, with estimates that there were dozens still there.

PolyU teams went in on Tuesday and Wednesday, but found only one young woman on Tuesday. Although a counsellor spoke to her, the woman did not leave the campus with the team and the university could not explain what happened to her.

Two weeks of chaos have left the campus in a bad state, with buildings damaged and vandalised, and petrol bombs, hazardous chemicals, rotting food and garbage left all over the place. Campus officials have called it a hygiene and health risk.

More than 1,000 radical protesters and their supporters occupied the campus a fortnight ago, and engaged in fierce battles with police on November 17. They hurled numerous petrol bombs, setting an armoured vehicle ablaze. A police officer was pierced in the calf after some in the mob fired bows and arrows.

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Police responded with tear gas and water cannons, sealed all campus exits and asked all those inside to leave.

About 1,100 people came out in the days that followed, although some escaped. Those over 18 were arrested, but about 300 minors only had their particulars recorded.

An unknown number refused to leave the campus, with some saying in the days that followed that they were afraid of being arrested and mistreated by police.

The force stayed put but, in a move to encourage the holdouts to leave, said those who needed medical treatment would not be arrested on the spot even if they were over 18. Their details would be recorded and police reserved the right to arrest them later.

Since Monday, PolyU’s leadership has called repeatedly for the police blockade to end. After failing to locate any holdouts, the university conceded it was possible that protesters still on campus could have avoided its search teams.

As late as 4pm on Wednesday, PolyU issued a statement asking yet again for police to leave, so that the last holdouts would come out. It asked “relevant departments” to help clean up the campus.

But a police source said the cordon had to stay because of the dangerous and potentially hazardous materials the team would have to deal with.

The source said police had been prepared to seek a court order to enter the campus if the university’s leadership made it difficult for them to go in.

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At 11pm on Wednesday, a masked man appeared in front of reporters on the campus, saying him and others he was in contact with were “extremely angry” about the police plan to enter.

After several days of outsiders, such as journalists, first-aiders and even suspected triad members, walking around site there was no evidence worth collecting, the man added.

“Police should respect the university’s request and retreat immediately and not challenge those protesters still inside, as well as Hongkongers’ bottom line,” he said.

The man said he was in contact with three of the fewer than 20 individuals he estimated to still be barricaded inside the campus. They were planning some form of action if police did come in, he said.

He also complained they had been harassed by suspected triad members, who he said posed as medics when they came to search for them.

“They pretended to be our brothers or medics at the beginning. They tried to break our room doors, and lure us to board the ambulances with all kinds of methods,” he said.

"Some of us dare not come out, and urinate inside our rooms.”

Many of them could not sleep well, the masked man added, because of those suspicious people who usually entered the site in a group in the small hours.

Earlier on Wednesday, law scholar Eric Cheung Tat-ming, legislator Ted Hui Chi-fung and several district councillors went to PolyU but did not spot any protesters either.

Hui said he had heard from a university source that the next step might be for police and firefighters to enter the campus, but he urged caution, saying some of the stragglers might respond badly if police were there.

Ho explained that the police team must remove dangerous items and offensive weapons such as petrol bombs and corrosive liquid, and gather evidence of the criminal damage to the campus.

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This was a task for the force, he said, and could not be left to the fire service because there were not only hazardous substances but also explosives on the campus. And because the team needed to gather evidence, detectives had been included.

He said that once the university informed police that the campus was severely damaged and there were a lot of dangerous items there, police had a responsibility to step in.

Ho gave an assurance that the force would adopt a peaceful and flexible approach in its work.

Asked what the officers would do if they came across protesters, he said: “We will convince them to leave, because they have stayed on campus for more than 10 days. We will promise them they can get medical treatment and then we will jot down their details.”

But he thought the possibility of finding any holdouts was low, given that PolyU’s search teams had already tried looking for two days.

A PolyU spokesman said that despite its best efforts, “searching every floor and every room of all buildings” its teams had drawn a blank.

“The university has done all it can to ensure that anyone remaining on campus could leave peacefully,” the spokesman said.