Chinese troops in Hong Kong have been deployed to help clear roads blockaded by anti-government protesters in a controversial move that could escalate the already high tensions in the Chinese territory.

Dozens of soldiers from the People’s Liberation Army (PLA), dressed in shorts and T-shirts, jogged from their barracks in Kowloon to the Hong Kong Baptist University where protesters had built barricades to stop riot police entering the campus. Joining a group of residents, they moved desks, signposts, and bricks blocking a road.

Throughout the past five months of demonstrations, the possibility of military interference and the spectre of Beijing’s past violent crackdown on student demonstrators in 1989 hung over the city.

The PLA, which stations approximately 12,000 of it staff in Hong Kong, can only be deployed to help with disaster relief or to maintain public order if requested by the local government.

RTHK English News (@rthk_enews) PLA soldiers are working at lightning speed to clear away bricks from the streets of Kowloon Tong. #HongKonghttps://t.co/qv37D9UeQQ pic.twitter.com/Ib8Kh8ROzq

During the 22 years since the former British colony was returned to Chinese control, the national military has only been seen on the streets once, to help with cleanup operations after a typhoon last year.

A group of protesters issued a statement titled “clearance today, crackdown tomorrow” criticising the cleanup effort as an “ill-disguised attempt to intimidate” them. “It is an entirely unacceptable act of invading Hong Kong’s promised autonomy,” the statement said. “This is a licence that opens up the perfect inroad for them to finally show their true colours.”

Experts say it is unlikely China would resort to such an extreme measure, which would invite widespread international condemnation. Beijing has repeatedly said it stands behind the Hong Kong government and police to handle the crisis.

On Thursday the Chinese leader Xi Jinping made his most direct remarks on the crisis, calling on Hong Kong to “restore order” and “severely punish violent criminals”.

Facebook Twitter Pinterest Anti-government protesters clash with the police outside the Polytechnic University in Hong Kong. Photograph: Thomas Peter/Reuters

Last week has seen a dramatic escalation of violence after two protest-related deaths and dozens of injuries. For five days, protesters paralysed transport links, vandalised mass transit stations and, in response to police storming several universities, turned campuses into fortresses, barricading entrances and stockpiling petrol bombs, bows, arrows, and catapults.

After a calm day, clashes erupted again on Saturday night as riot police fired teargas at protesters near Polytechnic University in Kowloon. Protesters shielded themselves with umbrellas and wooden boards and threw petrol bombs, lighting the ground, littered with bricks and other objects, on fire. Several injured protesters were seen being helped by first aiders.

Several universities in Hong Kong have cancelled classes for the rest of the semester and foreign students from the UK, Australia, Taiwan, and Europe have been encouraged to return home. Mainland Chinese students have also been evacuated.

Earlier on Saturday, traffic was returning to normal after some previously blocked roads were cleared. At the University of Hong Kong, protesters had destroyed a metro station exit near the school. Dozens of local residents, heeding a call from a Maxine Yao, a district council election candidate, were removing barricades that protesters had set up in the road.

Black-clad protesters wearing masksattempted to stop the cleanup but were outnumbered and forced to retreat to a footbridge overlooking the road. Protesters dropped several petrol bombs on the group but no one was hit.

Residents said they disagreed with the protesters’ methods and were tired of the disruption to their daily lives. Others chanted along with protesters, yelling “stand with Hong Kong.”

“They block the roads and take all of Hong Kong hostage to protest with them,” said Lydia, 40, who works in finance and lives in an apartment complex just outside the university.

“I felt sympathy for them for one and a half months. They have the right to do peaceful demonstration. Now the things they are doing have nothing to do with what they claim they are fighting for,” she said.

Heron Ho, 43, an alumnus of the university, criticised the methods of the protesters, many of whom are students. “I love the students but they do not know what they are doing,” he said. “This is not the way … they are destroying Hong Kong.”