Lam said a police safety group had been set up, consisting of secondary school principals, psychologists, social workers, paramedics, and trained negotiators to deal with the situation in PolyU, but they would only be called upon if the university failed to break the deadlock.

“We will only enter the campus in an appropriate time, hoping not to provoke people inside,” she said. “I hope the group doesn’t need to be deployed, if PolyU’s working team can successfully persuade people to leave the campus safely. The mission is still about persuading them to come out.”

Lam said she was aware of the tense relationship between police and protesters and that was why they had adopted “cooling” measures.

When asked about pan-democrat calls to release those who remained, she said it was a “law reinforcement” issue, and already 1,100 protesters had been handled under this principle.

In a bid to end the stalemate, police on Monday announced they would no longer immediately arrest those willing to leave, regardless of age, as long as they required medical treatment, although they could be arrested later. Previously, only those below the age of 18 were spared from immediate arrest.

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A police source said while officers had intended to join the PolyU team when it entered the campus, the university’s management had been reluctant for that to happen.

“They do not want police to join them going to the campus, as they don’t want to be seen as betraying the students,” the source said, adding the force did not intend to enter until after the PolyU team has finished.

PolyU said in its latest statement that its six teams had searched four buildings by 1pm on Tuesday, but did not find any protesters. They found that many parts of the buildings had been vandalised and destroyed, and different kinds of dangerous items and petrol bombs had also been discovered inside.

A police spokesman said police were aware of the PolyU team’s work and had been keeping close contact with the university.

A team of experts, assembled from various sectors by police, was on standby near the campus and would provide help if needed, the spokesman said.

Reiterating police’s flexible and peaceful approach, he added that those with medical needs would not be arrested on the spot, regardless of their age, and would first be given help.

“For those who leave the campus and do not have medical needs, police will enforce the law following existing mechanism and re-emphasise that they are guaranteed fair treatment,” the spokesman said.

PolyU earlier on Tuesday morning said in a statement that its teams would go through every building floor by floor, and that it hoped to complete the search in one day.

The statement, signed by PolyU council chairman Lam Tai-fai, president Teng Jin-guang and others from the senior management team, said hygiene inside the campus had worsened.

Speaking on a radio programme on Tuesday, Lam said he believed those still inside the campus were “afraid of police”.

Lam said he hoped the university’s team would offer more confidence to protesters than police, and thought more would be more willing to leave with them.

“I believe our team will bring a positive impact,” he said. “Our teams will be working on our own, we have no idea how police are going to carry out their operations.

“I think police should consider whether [their team] would bring a positive impact or whether it’d be counterproductive.”

In its fifth statement on Monday, issued shortly before midnight, PolyU management said several groups, including staff, counsellors, medical professionals, social workers and security personnel would look for individuals still on campus on Tuesday. Those involved would try their best to get them to leave in a peaceful manner.

PolyU again urged police to end the siege so repairs to the university buildings could be started immediately.

Shortly before midnight on Monday, education sector lawmaker Ip Kin-yuen said two of the radicals still in hiding appeared to be in good shape when he met them.

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At about 4.10am on Tuesday, a masked radical approached the media still on site and said he was grateful to people who had supported them, including those who had assembled near the campus on Monday evening, as well as the visiting lawmakers and district councillors.

He also displayed a number of Post-it notes with encouraging messages stuck on the door of the room he had chosen to hide in when volunteers had entered the campus.

Some of the messages read: “Not one [protester] less, go home together”, and “keep your life, please trust me for once”.

The man called on other anti-government protesters not to sacrifice any more for them.

“We’re happy staying here as we’ve got used to it,” he said. “There’s no need to worry about us.”

It was not known whether he was one of the protesters visited by Ip and other district councillors in the afternoon.

Police last week said those aged over 18 would be arrested on suspicion of rioting, but ­minors would have their information recorded before being let go.

Since then, more than 1,100 surrendered, had their details ­recorded, or were caught and ­arrested. The total included about 300 minors. PolyU said on Monday that only 50 were its students.

Many emerged after school principals, religious leaders, social workers and others went into the campus and ­persuaded them to leave. Several others ­escaped, while around 30 are estimated to remain in hiding.

Additional reporting by Kathleen Magramo and Chan Ho-him