Protests have swept Hong Kong since June as many in the city of 7.5 million people have vented fury at eroding freedoms under Chinese rule.
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.
Clashes between protesters and police have become increasingly violent.
Students and other protesters have taken over major campuses in Hong Kong this week, building barricades and stockpiling gasoline bombs and other weapons.
More people have been critically injured this week, than at any point in the long-running movement, with Hong Kong's Hospital Authority saying 67 people were treated in hospitals in total on Wednesday with injuries related to the protests.
"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. Some held up posters stating "Police we stand with you", while others chanted "Support the police". Some remained but in much smaller numbers.
Chinese troops have appeared on local streets only once since the 1997 handover, to help with cleanup operations after a typhoon in late 2018.
This has been the scene every lunchtime since the week began, in an area considered to be Hong Kong's Wall Street.
The Chinese government has unswerving determination to protect national sovereignty, security and development interests, implement "one country, two systems" policy and oppose any external force in interfering in Hong Kong's affairs, Xi Jinping said. Arguments and scuffles also broke out on Saturday between pro-government and pro-democracy activists during clean-ups across the city.
The number is not publicly known, but past estimates have put it at 8,000 or 10,000.
To watch Oliver Farry's report from Hong Kong's Polytechnic University, click on the player above.
"If the university can not continue to fulfil its basic mission and tasks, we must seek the assistance of relevant government departments to lift the current crisis".
Hundreds of residents moved in to help clear barricaded roads near several universities. Protesters have written online that they would break into mainland students' dorms and professors' offices to check for Chinese flags. No soldiers appeared to have been involved in the confrontations. I was anxious and scared after I realised what had happened and most protesters had left.
In a statement issued by the government in early hours of Friday, Cheng denounced all forms of violence and radicalism, and deprivation of others' legitimate rights in the pretext of pursuing some political ideals. "It's time for all the people who are silent to step up and say that's enough", said a 49-year-old housewife surnamed Kong. A 70-year-old man has died after being hit by a brick allegedly thrown by protesters.
Later that day a man shouting pro-Beijing slogans at protesters on a walkway was doused in flammable liquid and set alight. The victim is in critical condition.
Protesters are also demonstrating against police tactics cracking down on the rallies.
Some train services which had been suspended earlier in the week were gradually resuming, the city's metro operator MTR Corp said on Saturday.
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