Members of the media run away from fire during clashes between protesters and police outside the university. Reuters

Police fired tear gas at protesters holding out at Hong Kong Polytechnic University as overnight clashes resumed on Sunday, and opposition lawmakers criticised the Chinese military for joining a cleanup to remove debris from streets.

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A large group of people arrived to try to clean up a debris-strewn roadway near the campus but were warned away by protesters.

A protester’s umbrella is seen on fire during clashes with police outside university in Hong Kong. Reuters

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.

The faceoff came hours after intense overnight clashes 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.

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Protesters, who occupied several major campuses for much of last week, have largely retreated, 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.

Protesters clash with police outside Hong Kong Polytechnic University in Hong Kong on Sunday. Reuters

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.

Police prepare to fire on protestors at the Hong Kong Polytechnic University in Hong Kong on Sunday. AP

Opposition lawmakers issued a statement criticising 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 city’s anti-government protests have been raging for more than five months.

Protestors react during a confrontation at the Hong Kong Polytechnic University in Hong Kong on Sunday. AP

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.