Hong Kong, July 22 -- Clashes involving Hong Kong's protest movement escalated violently late Sunday as police launched tear gas at protesters who didn't disband after a massive march and subway riders were attacked by masked assailants who appeared to target the pro-democracy demonstrators.

The firing of tear gas was the latest confrontation between police and protesters who have taken to the streets for almost two months to fight a proposed extradition bill and call for electoral reforms in the Chinese territory.

The march had been peaceful when it reached its police-designated end point in Hong Kong's Wan Chai district in the late afternoon, but thousands continued onward, at various points occupying key government and business distr...