The one-minute video, which appears to have been filmed by the fornicating couple mid-tryst, has garnered millions of views on Weibo, China's answer to Twitter, and the mobile messaging service WeChat since it was posted on Tuesday. (link was here)

Censors moved quickly to pull down the clip and China's internet watchdog slapped Weibo and WeChat executives with an official reprimand for allowing the video to proliferate.

At first glance the location of the video is a mystery. The change room is unremarkable, with the noted exception of a man and woman engaged in vigorous sexual intercourse.

But an announcement over the store's speakers soon identifies the store as Uniqlo's flagship outlet in Beijing, at the Sanlitun shopping centre.

Moments after the male is heard whispering into his partner's ear "call me husband" and "say we'll be together", the intercom kicks in: "Dear customers, welcome to the Uniqlo store at Sanlitun".

"There are no fitting rooms on the first floor. Please proceed to the second and third floor if you need to try clothes on," a female voice announces.

The video appears to have become a publicity boon for Uniqlo, with a continuous stream of visitors taking selfies outside the Sanlitun store and searching for the infamous change room, within 24 hours of the video going viral, CNN reported.

The video has sparked a host of cheeky responses. Commemorative T-shirts featuring the image of the couple with the Uniqlo logo emblazoned across the woman's breasts were available in four colours for 35 yuan ($7.60) on the online fashion store Tao Bao.

But the Cyberspace Administration of China condemned the video as "unsocialist" and promised a clampdown on such "vulgar" material on the country's tightly controlled social media sites.

"The viral circulation of the obscene fitting room video on the internet has severely violated socialist core values," the agency cited an unnamed official as saying.

Uniqlo did not escape reprisal, with the watchdog suggesting the act was a publicity stunt.

"Highly concerned web users have reprimanded the acts that are suspected vulgar marketing or event marketing and have called for severe punishment," the CAC spokesperson said.

But the Japanese retail giant denied claims the 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," Uniqlo said in a statement on its website.

"We also firmly deny some online allegations saying the video is our publicity stunt."

Uniqlo said it immediately reported the indecent content to the social media sites that carried the video.

Beijing police are reportedly investigating who was responsible for filming the video, which clearly shows the faces of the pair involved in the sexual act, and who posted it online.