TAIPEI—China’s #MeToo advocates for accountability in cases of sexual misconduct have often run up against a state more concerned about preventing disturbances to public order.

Now, they see a breakthrough in the detention of one of China’s most recognizable movie stars.

Beijing police said late Saturday that they had detained Kris Wu, a pop star who is one of the country’s best-known celebrities, for what they called suspected rape. Authorities said they had responded to allegations that he repeatedly deceived young women into having sex with him.

The detention of Mr. Wu, a Chinese-Canadian singer and actor who is also known as Wu Yifan, was widely celebrated by Chinese internet users and even by Communist Party mouthpiece People’s Daily, which weighed in on its social-media account saying the more famous someone is, the more self-discipline they should exercise.

Before the police announcement, Mr. Wu denied the allegations and said he would willingly go to jail if they were true. A rape conviction in China usually results in between three and 10 years of prison. His lawyer and management company didn’t respond to requests for comment Sunday.

Though #MeToo accusations—targeting powerful men alleged to have taken advantage of their positions to abuse women—have spread around the world since gaining traction in the U.S. four years ago, the movement has met resistance from the Chinese government, which is wary that grassroots advocacy might disturb public order and bring down people in power.

Official word of the police detention, announced on China’s Twitter-like Weibo platform, received more than 1 million likes and appeared to offer a sense of catharsis after allegations about Mr. Wu’s behavior began piling up in June and July.

On July 8, Du Meizhu took to Weibo to accuse Mr. Wu of intoxicating and then having sex with her in December, when she was an 18-year-old college student. Ms. Du alleged that Mr. Wu lured other women with the prospect of exposure in the entertainment industry and gave some the impression he wanted to date them.

Ms. Du sparked a public furor against Mr. Wu, including from at least four women who similarly accused Mr. Wu of wooing them dishonestly.

Meantime, the July 8 post that initially detailed Ms. Du’s allegations has since disappeared from her account, for reasons that couldn’t be determined. Ms. Du didn’t respond to requests for comment Sunday.

Mr. Wu first shot to fame as a member of the South Korean-Chinese boy band EXO. As he made his name in recent years as a solo artist and as a star in mainland Chinese box office hits, his social-media following on Weibo climbed to more than 51 million followers.

Mr. Wu was hired as the face of high-profile global brands, but in recent weeks, as Ms. Du’s allegations came to light, many of them, including Louis Vuitton, Porsche, Bulgari and Lancôme, severed their relationships with him.

It is rare for Chinese authorities to move against someone so high profile for allegations of sexual harassment, let alone in such a public fashion.

In another closely watched sexual misconduct case involving a television news anchor and a former intern named Zhou Xiaoxuan, authorities initially attempted to silence Ms. Zhou, sending police to visit her parents.

Ms. Zhou sued the anchor in 2018, but court trial proceedings have dragged on without a verdict. Earlier this month, Ms. Zhou’s Weibo account, where she shared news about her case and occasionally voiced support for women’s rights, was suspended for breaking the platform’s rules. Weibo didn’t respond to a request for comment.

China’s #MeToo advocates believe Ms. Zhou’s case is particularly sensitive because the accused host works for state broadcaster Chinese Central Television. She says the host forcibly groped and kissed her, while he says he never touched her.

Mr. Wu, by contrast, isn’t directly tied to the state and is a Canadian citizen—the latter point being one that Chinese internet users, as well as People’s Daily, have played up.

Some online commenters have called for Beijing to not only send Mr. Wu back to Canada but to exchange him for Meng Wanzhou, the Huawei Technologies Co. chief financial officer who has been stuck in Canada for more than two years as she fights an extradition request from the U.S. Justice Department.

Mr. Wu’s detention comes as Chinese authorities rein in sky-high paychecks in the entertainment industry and investigate potential tax fraud, extramarital affairs, drug use and other alleged misconduct.

Some of the early reaction to allegations against Mr. Wu came from Chinese Communist Party-backed Legal Daily and the social-media account of the party’s Youth League, which urged calm, calling for the case to be settled by law rather than by online public opinion.

Beijing police first said on July 22 that they were investigating Mr. Wu, and had already confirmed some details, including sex between him and Ms. Du at a work-related event at Mr. Wu’s home, where people were drinking.

Saturday’s announcement of Mr. Wu’s detention sparked a celebratory reaction on China’s closely regulated internet, where comments supporting women’s rights are often censored. Replies to Saturday’s police announcement praised authorities’ action and Ms. Du’s bravery.

“It’s finally here,” read one comment, while another read: “The police have worked hard. Thank you for your justice. Hang in and don’t let go.”

Signs of online support for Mr. Wu were scarce, although some called on people to wait for the results of the official investigation before coming to any judgment.

Lü Pin, a Chinese women’s rights activist, said Mr. Wu’s detention was surprising, given Chinese authorities’ usual reluctance to investigate rape allegations brought by women, particularly when the accused and accused know each other. Ms. Du in her account said that she and Mr. Wu had dated for a short period after the alleged rape incident. She said she later came to believe dating her was part of his strategy to trick her.

“If police don’t investigate, there’s very little victims can do,” said Ms. Lü. “That’s why this is a huge encouragement to women.”

Ms. Zhou, the former CCTV intern, said in an interview Sunday that she has been encouraged by the bravery of women who have come forward against Mr. Wu.

“More and more people are willing to express their trust in women in public,” she said.

—Qianwei Zhang and Zhao Yueling contributed to this article.

Write to Chao Deng at Chao.Deng@wsj.com