Dozens of exhausted pro-democracy protesters occupying a Hong Kong university defied warnings to surrender Tuesday on the third day of a stand-off with police, as China sent fresh signals that its patience with nearly six months of unrest was running out.

Fearing arrest or being shot at by police, a dwindling number of protesters remained huddled inside Hong Kong Polytechnic University (PolyU) as night fell.

The siege at PolyU began Sunday with many hundreds of protesters occupying the campus as part of a broader campaign of massive disruption across Hong Kong that began last week.

The ensuing confrontation turned into the most intense and prolonged of Hong Kong's pro-democracy crisis, which has seen millions take to the streets since June to voice anger at China's erosion of the territory's freedoms.

During the siege protesters had repelled police surges with a barrage of Molotov cocktails, arrows and bricks. Police in response threatened to use live rounds.

Some protesters escaped overnight on Monday by shinning down ropes from a footbridge to a road, where they were whisked away on motorbikes.

Others disappeared into manholes to try to probe the drainage system for a route out.

ArrestsIn an apparently co-ordinated effort to distract police, tens of thousands of people streamed towards the PolyU campus on Monday night as clashes simultaneously raged with police in nearby Kowloon district.

- New phase of violence -

Footage on Monday showed armoured police beating fallen protesters with batons as they lay on the ground.

One officer was filmed stamping on the head of a man who was already subdued.

Alleged police brutality is one of the central complaints of the protest movement. Senior officers insist their men are acting proportionately.

In her first public comments on the PolyU crisis, Hong Kong chief executive Carrie Lam said surrender was the only way to achieve a peaceful outcome.

"This objective could only be achieved with the full cooperation of the protesters, including of course the rioters.

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"They have to stop violence, give up the weapons and come out peacefully and take the instructions from the police," she said.

Lam said children who surrendered would not be arrested, though protesters aged over 18 would face charges of rioting.

About 1,000 people had been arrested throughout Hong Kong over the previous 24 hours, Chief Superintendent Kwok Ka-chuen said on Tuesday afternoon.

This was roughly a fifth of all arrests since the unrest began in June.

Kwok said those arrested included some who had abseiled from the footbridge, as well as motorcyclists who helped them.

And in an apparent contradiction of Lam, Kwok insisted everyone would feel the force of the law.

"No excuse, no political demand or motive can spare anyone from legal liability," he said.

"Regardless of their age and causes, they are to face the consequences of their own actions."

- Determination -

With police custody their best option, some inside PolyU were determined to fight on.

"Even if we surrender they will still put us to jail. It seems we have two options, but actually we only have one... which is jail," one of the protesters, a mechanical engineering student who gave his name as Matthew, told AFP inside the campus.

But their numbers were dwindling. AFP reporters on site estimated up to 100 remained by late afternoon.

The new phase of mass disruption, which began last week, has caused chaos throughout the international financial hub, with schools closed, train lines disrupted and major roads blocked by barricades.

With the crisis deepening, China's ambassador to Britain upped the ante on Monday.

"If the situation becomes uncontrollable, the central government would certainly not sit on our hands and watch," Liu Xiaoming said. "We have enough resolution and power to end the unrest."

In another ominous signal, China insisted Tuesday it had sole authority to rule on constitutional matters in Hong Kong, which it rules under a special model giving the city greater freedoms than enjoyed on the mainland.

The warning came as it condemned a decision by the city's high court on Monday to overturn a ban on face masks worn by pro-democracy protesters.

Only China's parliament has the right to rule on Hong Kong's Basic Law -- the city's mini-constitution, parliament spokesman Zang Tiewei said.

"No other institution has the right to make judgements or decisions," he said.

A mainland scholar who requested anonymity to speak freely about such a sensitive subject said while the parliament had the right to take away what it gave, the timing of the announcement was ill-advised.

"Such a statement would gravely affect people's views on the principle of 'One Country, Two System'."

Carrie Lam has repeatedly insisted that her unpopular police force can contain the unrest, and said Tuesday there was currently no need for the People's Liberation Army to intervene.

Protests started in June as a peaceful condemnation of a now-shelved China extradition bill.

They morphed into a broader movement to defend the city's unique freedoms, which were meant to be enshrined in the Basic Law when Hong Kong was handed over by Britain in 1997.

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