HONG KONG >> Hong Kong police water cannon trucks drove over bricks and nails strewn by protesters and sprayed them at close range Sunday, as opposition lawmakers criticized the Chinese military for joining a cleanup to remove debris from streets.

Other officers fired tear gas in a bid to drive out a determined group of protesters on the streets outside Hong Kong Polytechnic University. The push came in an hourslong standoff that followed intense clashes the previous night.

A large group of people arrived in the morning to try to clean up the road, but were warned away by protesters.

Riot police lined up a few hundred meters (yards) away and shot several volleys of tear gas at the protesters, who sheltered behind a wall of umbrellas across an entire street and threw gasoline bombs into nearby bushes and trees, setting them on fire.

The water cannons arrived in the early afternoon, one using blue-dyed water to drench the protesters.

The daytime faceoff came after a pitched battle at night in which the two sides exchanged tear gas and gasoline bombs that left fires blazing in the street. Many protesters retreated inside the Polytechnic campus, where they have barricaded entrances and set up narrow access control points.

Protesters have largely retreated from occupations of several major campuses last week, except for a contingent at Polytechnic. That group is also blocking access to the nearby Cross-Harbour Tunnel, one of the three main road tunnels that link Hong Kong Island with the rest of the city.

Elsewhere, workers and volunteers — including a group of Chinese soldiers who came out from their barracks — cleared roads of debris Saturday as most of the protesters melted away.

There were scattered incidents of protesters arguing and clashing with people clearing roadways, and in one instance, throwing a gasoline bomb near City University of Hong Kong.

Opposition lawmakers issued a statement criticizing the Chinese military for joining the cleanup. The military is allowed to help maintain public order, but only at the request of the Hong Kong government.

Dozens of Chinese troops, dressed in black shorts and olive drab T-shirts, ran out in loose formation near Hong Kong Baptist University and picked up paving stones, rocks and other obstacles that had cluttered the street

The Hong Kong government said that it had not requested the military’s assistance, describing it as a voluntary community activity.

The Education Bureau announced that classes from kindergarten to high school would be suspended again on Monday because of safety concerns.

Classes have been canceled since Thursday, after the bureau came under criticism for not doing so earlier.

The city’s anti-government protests have been raging for more than five months.

They were sparked by a government decision to submit legislation that would have allowed the extradition of criminal suspects to the mainland. Activists saw it as an erosion of Hong Kong’s autonomy under the “one country, two systems” formula implemented in 1997, when Britain returned the territory to China.

The bill has been withdrawn, but the protests have expanded into a wider resistance movement against what is perceived as the growing control of Hong Kong by Communist China, along with calls for full democracy for the territory.