HONG KONG — Trash on beaches is an unwelcome reality for people in Hong Kong, as it is in many places in the world. In recent days, however, the city’s shores have been inundated by an overwhelming amount of debris, prompting public complaints and a search for the source of the refuse.

Hong Kong’s top official, Chief Executive Leung Chun-ying, said that mainland China was partly to blame. “We’ve seen an unusual phenomenon in recent weeks that lots of domestic garbage from the mainland has washed up in Hong Kong, which we estimate could be related to heavy rainfall and flooding,” he said on Sunday as he and a dozen high-ranking officials picked up trash on Lantau Island.