Chinese police have detained five people over a sex video filmed in a Beijing store of the popular fashion retailer Uniqlo, media reports said.

"Five people were taken away by police including the man and woman who played the main role," state-run broadcaster Beijing Television reported, according to South China Morning Post.

A selfie sex video featuring a young couple having sex in a fitting room of Uniqlo's Beijing store was posted online last week. The one-minute video has gone viral on social media since its first appearance on social messaging app WeChat on Tuesday night. In the video, the man, wearing glasses, a black T-shirt and jeans, is heard telling the naked woman to kiss him and call him "husband" while taking selfie video on his iPhone in front of the fitting room's mirror, according to ECNS.

Japanese-owned Uniqlo on Wednesday denied the allegations that the sex video was a publicity stunt.

"We would like to remind the public to uphold social morality and use our fitting rooms in a correct and proper way. We also firmly deny some online allegations saying the video is our publicity stunt," Uniqlo said in the statement, according to Shanghai Daily.

China's Internet watchdog reprimanded executives from Weibo and WeChat for allowing spread of pornographic film.

"The vulgar video had spread like a virus online and clashed with socialist core values. The government would continue to crack down on vulgar materials online and safeguard the cyber environment," said Xu Feng, a director at the Cyberspace Administration of China, AsiaOne reported.

"Both the man and the women in the video are in the wrong," a Beijing-based lawyer Liu Ning told Beijing TV, according to The Guardian. "Fitting rooms provide some level of privacy but they are still public places. This kind of behaviour in a public place is inappropriate and could even violate public security management regulations."