Hong Kong police have fought running battles with protesters trying to break a security cordon around a university in the city, firing teargas both at activists trying to escape the besieged campus and at crowds trying to reach it from outside.

Police have said the demonstrators inside Polytechnic University had no option but to come out and surrender.

The sprawling campus has been occupied by demonstrators since last week, and has become the focus of the most prolonged and tense confrontation between police and protesters in more than five months of unrest in the semi-autonomous city.