A police officer was struck by an arrow fired by a Hong Kong protester on Sunday and an armoured vehicle set ablaze, as fires raged into the night around a campus which has turned into a base for a pro-democracy movement that has sunk the city into turmoil.
Protests have tremored through the global financial hub since June with many in the city of 7.5 million people venting fury at eroding freedoms under Chinese rule.
China has repeatedly warned that it will not tolerate the dissent, and there have been concerns that Beijing could send in troops to put an end to the unrest.
Chinese President Xi Jinping this week issued his most strident comments on the crisis, saying it threatened the "one country, two systems" model under which Hong Kong has been ruled since the 1997 handover from Britain.
On Sunday night activists dug in around Hong Kong Polytechnic University (PolyU), setting large fires to prevent police from conducting a threatened raid on the campus.
An armoured vehicle was hit by a flurry of petrol bombs as it edged towards protesters on a flyover near the campus, while a nearby footbridge was set ablaze.
Police declared the campus a "riot" scene -- a rioting conviction carries up to 10 years in jail -- and blocked exits threatening "new operations" against those left inside.
But protesters appeared resolute -- a twist in tactics by a leaderless movement so far defined by its fluid, unpredictable nature.
"I feel scared. There's no way out, all I can do is fight to the end," said one protester joining the barricade in front of the university building.
We need a base to keep our gear and have some rest at night before another fight in the morning," another called Kason, 23, told AFP.
Earlier, activists parried attempts by police to break through into the PolyU campus, firing rocks from a homemade catapult from the university roof.
An AFP reporter saw a team of masked archers -- several carrying sports bows -- patrolling the campus.
Police shared images of an arrow embedded in the calf of an officer outside the campus and decried the use of "lethal weapons," declaring the campus a "riot scene".
Video showed a photographer with a local media outlet apparently knocked unconscious after being hit by a stream from a police water cannon.
A statement from the outlet posted online said he suffered a "serious head injury".
Violence has worsened in recent days with two men killed in separate incidents linked to the protests this month.
Clashes rippled out across the city deep into Sunday night, with protesters trading Molotov cocktails with tear gas fired by police. Activists have vowed to wreak further havoc on Monday.
Demonstrators last week engineered a "Blossom Everywhere" campaign of blockades and vandalism, which forced the police to draft in prison officers as reinforcement, shut down large chunks of Hong Kong's train network and close schools and shopping malls.
The movement, characterised by its fluidity and unpredictability, has started to coagulate in fixed locations, showing their ability to switch tactics.
The protests started against a now shelved bill to allow extradition to China but have billowed to encompass wider issues such as perceived police brutality and calls for universal suffrage in the former British colony.
The financial hub has been nudged into a recession by the unrelenting turmoil.
Hong Kong's airport authority on Sunday said October traffic figures were down 13 percent on last year with 5.4 million passengers as the economy takes a battering.
A poster circulating on social media called for the "dawn action" to continue on Monday.
"Get up early, directly target the regime, squeeze the economy to increase pressure," it said.
The education bureau said schools will remain closed again on Monday.
Earlier on Sunday, dozens of pro-government supporters gathered to clear barricades near the university campus -- a sign of the divisions slicing through the city.
Many residents are wearied by the sapping protests. Others support the Chinese-backed city government.
Some applauded a Saturday cameo in a clean-up by Chinese troops from a garrison of the People's Liberation Army in Kowloon.
The garrison is usually confined to the barracks under Hong Kong's mini-constitution, although it can be deployed under the request of the city's government to help with public order breakdown or natural disasters.
Hong Kong government, which presides over a city that enjoys greater freedoms than the mainland, said it did not ask the PLA for help on Saturday.
The choreographed troop movement "has only compounded the impression that Beijing has simply ignored" Hong Kong's unique political system, said analyst Dixon Sing.