BEIJING — One late September afternoon, Sun Shihua, a lawyer, walked into a police station in southern China for a routine visit with a client.

What happened next is now the subject of wide debate in China.

Ms. Sun says that a male police officer choked and beat her after getting into an argument over credentials, and then forced her to submit to a strip search. In a social media post that was widely shared this week, she called the episode “the darkest, most terrifying and humiliating day of my life.”

The authorities in Guangzhou, the southern Chinese city where the events are said to have taken place, deny any wrongdoing, saying they have security camera footage that challenges Ms. Sun’s claims.

The case has revived concerns in China about police brutality and a lack of transparency in law enforcement, after a series of high-profile cases of abuse at the hands of police officers.