Despair, frustration and fear set in among the last remnants of student protesters in Hong Kong’s besieged Polytechnic University on Tuesday, but a flicker of defiance still ran strong among the small group, as they vowed to continue their four-day standoff with the police.

In the trashed campus canteen, plastic litter and uneaten food strewn on the linoleum floor, some half dozen young men and women still wore black body armour and talked in hushed tones while one repeatedly punched a pillar and another toyed with a bow and arrow.

In another corner, Mark Wong, 21, his face covered with a white dish cloth, sat with two female companions, hunched over their phones as they plotted potential escape routes.

They appeared to have lost their moment. Several dozen are believed to have escaped on Monday by climbing over walls, abseiling down ropes to waiting motorbikes or laying low in nearby buildings before blending into the crowd. By 11pm on Tuesday, around 800 people had voluntarily surrendered, said the police.

Most were arrested, but some 300, all minors, had their information recorded by officers but were allowed to go home after successful negotiations by school principals.