HONG KONG — Hundreds of Hong Kong activists armed with firebombs and bows-and-arrows on Monday battled riot police who have laid a days-long siege to a university, the most violent confrontation yet in a half-year of protests.

Early Monday, the police tried storming the campus at the main entrance and made some arrests. But the occupiers fought back with dozens of firebombs and set barricades ablaze, forcing the police to retreat.

As day broke, the occupiers and the police were still locked in the standoff at Hong Kong Polytechnic University that began Saturday night, and smoke billowed from the grounds. Some protesters on Monday morning raced for the exits, only to be met with volleys of tear gas.