Beijing police are holding six people who are allegedly involved in a sex video that was apparently made in a popular fashion retailer's fitting room, Beijing media reported on Sunday.

The six include a man and woman suspected of being in the video, which was made in April in the Uniqlo outlet in Beijing's Taikoo Li Sanlitun shopping center, Beijing police said on their micro blog on Sunday.

A man surnamed Sun, 19, one of the six, is detained for uploading the video to Sina Weibo, China's Twitter-like social network. Three others are detained for spreading the video, police said.

The man and the woman in the video are still under investigation, say police.

Police in the capital's Chaoyang district, where the Sanlitun area is located, started to look into the case last week when the video went viral on social media including WeChat and Sina Weibo.

As the investigation continues, the one-minute video, allegedly showing the man and woman having sex, has been quickly removed from the Internet, and related pictures have been deleted.

Uniqlo said in a statement on its micro blog on Wednesday that it is paying attention to the case and denied that the incident was a corporate publicity stunt.

The retailer said it had reported the case to government officials and advised customers to "properly use its fitting rooms".

The Cyberspace Administration of China, the nation's top Internet watchdog, later summoned managers of Sina and Tencent, which run Sina Weibo and WeChat, and ordered them to improve their management to curb the spread of lewd media.