HONG KONG (Reuters) - Thousands of demonstrators blockaded police headquarters on Friday as Asia's leading financial centre braced itself for a third weekend of mass protests against an extradition bill that has plunged the Chinese-ruled city into crisis.

Groups of mostly students wearing hard hats, goggles and face masks set up roadblocks and trapped vehicles in a generally peaceful protest to demand that leader Carrie Lam, who promoted and then postponed the bill, scrap it altogether.