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.


At least 12 killed in Nigeria mining site attack
UN, aid groups warn Gaza operations at risk from Israel impediments
Israel approves natural gas deal with Egypt, Netanyahu says
US approves $11.1 billion largest-ever arms package for Taiwan
Trump adds seven countries to full travel ban list
