HONG KONG (AP) — Overturned chairs. Empty plastic bottles scattered around. Food leftovers rotting in the canteen.

Most of the protesters who took over the Hong Kong Polytechnic University have left following clashes with police, but an unknown number have remained inside, hoping somehow to avoid arrest.

Six masked protesters surrendered before dawn Friday, bringing to about 30 the number that have come out the previous day from the campus surrounded by police.

Tang Chun-Keung, head of the Hong Kong Association of the Heads of Secondary Schools, said that the holdouts include minors, numbering less than 10, and they are emotionally unstable. Tang entered the campus Friday with some others but failed to find them.

“We have lawyers and social workers ready to provide assistance and we hope to persuade them to leave the campus. We are worried our work is getting more and more difficult because students are refusing to meet us,” he told reporters.

Police Commissioner Tang Ping-keung said that those under 18 can leave, although they may face charges later, and pledged impartial treatment for all adults facing arrest.

“The condition is deteriorating and dangerous, there are many explosives and petrol bombs inside … we hope to end the matter peacefully,” he said, adding police haven’t set any deadline to end the siege.