HONG KONG — This city’s Ming Pao newspaper has long stood for sober independence in a media market that is both brashly commercial and buffeted by political winds from China, its reporters pursuing and often breaking stories that irk the territory’s overseers in Beijing.

So when the paper’s chief editor, Kevin Lau Chun-to, told employees this month that he was being moved aside by its owners, the suspicion spread that he had been sacrificed to appease the Chinese government and its local loyalists. Shock rippled through the newsroom. Noisy protests broke out among residents who fear that Mr. Lau’s abrupt departure represents an alarming advance in the Chinese Communist Party’s efforts to subdue the territory’s independent media.

His ouster comes as Hong Kong enters a volatile time, facing contention over how far to go in proposals to elect the territory’s leaders through universal suffrage, a step that worries the Chinese government, as well as broader tensions about the growing political and social influence of mainland China. For many, the shake-up at Ming Pao crystallized anxieties about those strains and about the vulnerability of the news media to political influence. On a recent weekend, hundreds of protesters gathered outside the newspaper’s offices, many dressed in black and clutching black balloons, calling for it to maintain its independence.

“If Ming Pao goes down, it does mean that the lights go out” on independent, aggressive reporting, said Margaret Ng, a lawyer who has worked as an editor at the newspaper and also served on the Hong Kong Legislative Council.