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.


US, German scientists win Nobel medicine prize for work on light and brain
Spanish PM Sanchez calls snap election for November 29
Hundreds of French schools stay closed ahead of nationwide day of student protests
Thousands of Imran Khan supporters start march to Pakistani capital, party says
US removes bombers from UK base at centre of suspected Iranian plot