Fiery clashes erupted across the city, with security chief John Lee cautioning "unthinkable" consequences if the violence continued.
Authorities have shut down schools, rail links and several businesses in the Asian financial hub as a safety precaution.
On Tuesday night, hundreds of black-clad protesters tried to block riot police from entering the Chinese University of Hong Kong (CUHK) near Tai Po by hurling bricks and petrol bombs.
UN: 70% of Gaza fatalities women and children
The UN Human Rights Office said on Friday nearly 70 per cent of the fatalities it has verified in the Gaza war were women and children, and condemned what it called a systematic violation of the fundamental principles of international humanitarian law.
Britain names Jonathan Powell as national security adviser
Britain on Friday named Jonathan Powell, who was chief of staff to former prime minister Tony Blair, as its national security adviser.
Indonesian volcano spews ash 10 km high
Indonesia's Mount Lewotobi Laki-laki erupted several times on Friday, belching volcanic ash that rose up to 10 km (32,800 ft) into the sky, officials said, following a big eruption on Sunday night that killed nine people.
Israeli PM directs two rescue planes to Amsterdam
Israeli Prime Minister Benjamin Netanyahu has directed two rescue planes to Amsterdam after being informed of "a very violent incident" targeting Israeli citizens, his office said on Friday.
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