HONG KONG — A sea of Hong Kong protesters marched through the dense city center in the pouring rain on Sunday, defying a police ban, in a vivid display of the movement’s continuing strength after more than two months of demonstrations, days of ugly violence and increasingly vehement warnings from the Chinese government.

People began assembling in the early afternoon in Victoria Park, the starting point of huge peaceful marches in June that were joined by hundreds of thousands of protesters. The police approved the Sunday rally but objected to plans to march to the Central district, citing clashes that had occurred after previous events. But protesters marched anyway.

By midafternoon, the park had filled with tens of thousands of people, and the demonstrators began to spill into nearby roads. Protesters holding signs jammed a multilane main road in the Causeway Bay shopping district, stopping traffic and forcing trams to slow to a crawl. The crowd inched toward the park amid heavy rain, shouting, “People of Hong Kong, keep fighting.”

Organizers estimated at least 1.7 million people had turned out — nearly one in four of the total population of more than seven million — making it the second-largest march of the movement, after a protest by nearly two million on June 16.