HONG KONG (AP) — Police have fired tear gas at protesters holding out at Hong Kong Polytechnic University as overnight clashes resumed in the morning.

A large group of people arrived Sunday to try to clean up a debris-strewn roadway. Riot police appeared after the cleaners were warned away by the protesters.

The police shot volleys of tear gas toward the protesters, who sheltered behind a wall of umbrellas across an entire street.

The skirmish came hours after intense overnight clashes in which the two sides exchanged tear gas and gasoline bombs. Many protesters retreated inside the Polytechnic campus.

Protesters have largely retreated from other major universities that were occupied for much of last week, but a contingent remains at Polytechnic.

Hong Kong’s anti-government protests have been raging for more than five months.