A young couple allegedly at the centre of a viral sex video that outraged Chinese authorities have been arrested, according to reports.

The one-minute video, which appears to have been filmed by the fornicating couple mid-tryst, was shot in the change room of a Uniqlo store in Beijing.

It went viral on China's tightly controlled social media after being posted online on Tuesday, garnering millions of views on Weibo (China's answer to Twitter) and mobile messaging service WeChat.

Censors moved quickly to pull down the clip, condemning it as "unsocialist" and "vulgar".

"The viral circulation of the obscene fitting room video on the internet has severely violated socialist core values," a official from China's internet watchdog said.

Police arrested five people in relation to the video on Wednesday night, just hours after the footage went viral, according to state-run broadcaster Beijing Television.

"Five people were taken away by police including the man and woman who played the main role," the channel reported.

"The police investigation has two main parts: who published this unsavoury video, and was it an example of hype by the business [Uniqlo]," it added.

The Cyberspace Administration of China slapped Weibo and WeChat executives with an official reprimand for allowing the video to proliferate. It also pointed the finger at Uniqlo, 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," a CAC spokesperson said.

The Japanese clothing retailer has firmly denied the claims, posting a statement on its website urging members of the public to "uphold social morality and use our fitting rooms in a correct and proper way".

However, it does appear that the video spurred something of a publicity boon for Uniqlo. Despite the authorities' outrage, many Chinese have responded with amusement - and no small dose of voyeurism.

Within 24 hours of the video being posted, a continuous stream of visitors were seen taking selfies outside the Sanlitun store and searching for the infamous change room, CNN reported.

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.