Thousands of people dressed in black marched in Hong Kong on Friday to press for the total withdrawal of a controversial extradition bill that has triggered violent protests and plunged the financial hub into political crisis.

Demonstrators, mostly students wearing hard hats, goggles and face masks, disrupted traffic on key roads in a mostly peaceful protest to demand that embattled leader Carrie Lam, who promoted and then postponed the bill, scrap it altogether.

"We want to fight for our freedom," said high school student Chan Pak-lam, 17, who was protesting in sweltering heat of about 30 degrees Celsius (86 Fahrenheit).