Police fired rounds of pepper balls at protesters in Hong Kong on Sunday as hundreds took to the streets to demonstrate against the postponement of legislative elections and a new national security law imposed by China.

Hong Kong leader Carrie Lam postponed the September 6 election for seats in the Asian financial hub’s Legislative Council for a year in July because of a spike in coronavirus cases.

The move dealt a blow to the pro-democracy opposition who hoped to win a historic majority in the council, where only half the seats are directly elected and the other half are appointed members who mostly support Beijing...