BEIJING — Hundreds of people took to the streets of a city in China’s southern Guangdong Province on Friday to protest a proposed uranium processing plant that would be the nation’s largest when completed.

Participants said that as many as 1,000 residents “took a walk” through Jiangmen, a city less than 60 miles from Hong Kong, to express their opposition to the plant, which officials say could enrich enough nuclear fuel to provide roughly half of China’s atomic energy needs by 2020.

Unsanctioned public gatherings are prohibited in China, but marchers said the police had largely held back as the crowd moved through the city carrying banners that read “Yes to Children, No to Nukes” and “Fight Nukes or Die!”

Organized through social media and billed as an innocent stroll through the streets of Jiangmen, the demonstration was the latest example of urban Chinese willing to defy the authorities over environmental concerns. The government would not be likely to tolerate a similar gathering to demand political reform or an easing of news media restrictions.