Police fired tear gas while protesters threw petrol bombs and fired arrows in clashes outside Hong Kong’s Polytechnic University on Saturday, just hours after Chinese soldiers made a rare appearance to help clean up the city’s streets.

China’s People’s Liberation Army (PLA) soldiers in shorts and T-shirts appeared in streets outside their base, helping residents clean up debris after anti-government protests blocked roads. The presence of PLA troops on the streets, even to help clean up, could stoke further controversy over the Chinese-ruled territory’s autonomous status.

A city spokesman said the Hong Kong government did not request assistance from the PLA but the military initiated the operation as a “voluntary community activity”.

Saturday’s clean-up followed some of the worst violence seen this year, after a police operation against protesters at the Chinese University of Hong Kong on Tuesday.

The authorities have since largely stayed away from at least five university campuses that had been barricaded by thousands of students and activists who stockpiled petrol bombs, catapults, bows and arrows and other weapons.

Many protesters appeared to have left the campuses by late Saturday but Hong Kong’s Cross-Harbour Tunnel was still blocked by protesters occupying Polytechnic University, where violence flared again on Saturday night.

“We don’t want to attack the police, we just want to safeguard our campus,” said Chan, a 20-year-old Polytechnic student. “The reason why we want to safeguard our campus is we want citizens to join the mass strike and protect Hong Kong.”

By late afternoon, the PLA soldiers had left the streets outside Baptist University beside their barracks in Kowloon Tong.

Chinese troops have appeared on streets only once since the 1997 handover to help clear up after a typhoon in 2018. It was not clear how many were involved on Saturday.

The PLA garrison in Hong Kong said that when some residents began cleaning, some troops “helped clear the road in front of the garrison gate”.

Demosist, a pro-democracy organisation, said Saturday’s clean-up operation could set a “grave precedent” if the city’s government invites the military to deal with internal problems.

In August, Beijing moved thousands of troops across the border into Hong Kong in what state news agency Xinhua described as a routine rotation. Foreign envoys and security analysts estimate up to 12,000 troops are now based across Hong Kong — more than double the usual garrison number.

Standing beside a black flag with the slogan “Liberate Hong Kong, Revolution of our Times”, James Wong, 23, was among protesters manning a bridge at Baptist University.

“We didn’t want to confront the people and the PLA troops directly,” he told Reuters. “We are not directly against the PLA, but rather the government. But the PLA should not leave their base because this is Hong Kong territory.”