A gold medalist diver’s mother said she was afraid for her daughter to come home after their hometown was swarmed with her supporters. A champion swimmer whose hotel was staked out by admirers disbanded his official fan group and told an interviewer he would rather have performed worse if it meant he would be left alone.

Other athletes have been hounded by crowds at airports or been the subjects of vicious arguments online between rival fan camps, leading Chinese official media to denounce fans for being “visibly aggressive.” The police have even detained at least two people for allegedly defaming athletes.

After a stellar run at the Paris Olympics, where China tied the United States for the most gold medals, Chinese athletes are now facing a darker side of that success: extreme fans.

Celebrities globally have to deal with fans who are sometimes invasive, but in China this phenomenon can be especially intense. Fan groups spend lavishly on products endorsed by their idols, deploy bots to ensure their favorites stay atop social media trending lists and even mount harassment campaigns against other stars and their supporters. Some fans stalk their idols and sell their photos or personal information.

At first, the obsession was directed mostly at actors and musicians. But in recent years, it has turned to athletes, too.

In southern China’s Guangdong Province, the village of Maihe, population a few thousand, has been flooded with over 1,000 visitors every day, according to Chinese media. They are there to see the home of Quan Hongchan, 17, who won two diving golds in Paris.

Village officials have built parking lots to accommodate the visitors. Snack vendors have flooded the street in front of her house. Videos on social media show people sitting on blankets on the street, posing with banners showing Ms. Quan’s face and taking photos of a cordoned-off house, as police officers stand nearby.

In a video that topped trending hashtags this week on Weibo, a platform similar to X, Ms. Quan’s mother said she “didn’t dare” let her daughter return home.

But staying away has done little to spare Ms. Quan the attention. When she arrived at a Beijing airport from Paris, people crowded around her, taking close-up photos of a visibly uncomfortable Ms. Quan or shoving flowers into her hands, widely shared videos show.

Other athletes have tried other ways to fend off the spotlight. Pan Zhanle, a swimmer who broke his own world record in Paris, shut down his only official fan account on Weibo. He did not give a reason for doing so, but in an interview with China’s state broadcaster, he said he was “definitely not happy” about the heightened attention, which had led mobs of fans to stake out his hotel.

“I’m still just myself,” he said. “I’d rather not have performed so well this time, so in the future I could continue training in peace.”

Perhaps the most extreme example of fandom gone awry occurred during the Games, when two Chinese players faced off in the women’s table tennis final. Fans of Sun Yingsha, who lost the match, viciously attacked the other player, Chen Meng, online. In Paris, Chinese fans also booed Ms. Chen.

State media quickly accused extreme fans of bringing shame to Chinese sports. A commentary in People’s Daily, the Communist Party’s mouthpiece, accused some fans of “losing their rationality.”

Experts interviewed by Chinese media said that the emergence of extreme fandom in sports was likely a reflection of the rising status of athletes as marketable stars. But they have also speculated that fans, many of them young, are lonely and seeking community.

Zhang Nan, an economist at Renmin University in Beijing, wrote in The Global Times, a party tabloid, earlier this year that China’s rapid economic development and urbanization had created a “new generation of atomized individuals.” “In the internet era,” Professor Zhang wrote, fan culture allows them to “fill the void.”

If the fandoms are more intense in China, the consequences can be too, given the government’s controls over speech and wariness of any perceived threats to social stability. For several years, the central government has declared war on what it calls toxic fandom, which it accuses of leading young people astray.

In recent days, Chinese social media platforms have said they removed tens of thousands of posts and banned hundreds of accounts for “inciting conflict.”

On Aug. 6, three days after the table tennis controversy, the police in Beijing announced that they had detained a 29-year-old woman for “maliciously fabricating information” about athletes and coaches online. The police in the city of Guangzhou said on Tuesday they had also detained a 38-year-old woman for slandering national team athletes and coaches.

The arrests may scare fans away from outright attacking rival stars. But there is little sign that other forms of star-chasing are fading.

On Wednesday, reports circulated on social media that the family of Ms. Quan, the diver, was living in a remote orchard to avoid the hubbub in their village.

It quickly became one of Weibo’s top trending topics.