Tourists admire the skyline view of Lujiazui area at the Bund in Shanghai, east China, Jan. 6, 2020. (Xinhua/Wang Xiang)

Shanghai's market regulator rolled out guidelines on Friday to regulate the mystery box market in the city.

Mystery boxes or blind boxes give a random item when opened, greatly popular among young people.

According to the city's administration for market regulation, the price of mystery boxes will be set to be no more than 200 yuan (about 31.5 U.S. dollars).

The guidelines also said that sellers should not sell these boxes to children under the age of eight, or carry out excessive marketing and speculation.

Sources with the mystery box giant Pop Mart expressed supportive attitude towards the guidelines and said that the company will cooperate with the regulator to explore feasible detailed schemes.

The new move comes after a statement made by the China Consumers Association on Wednesday, noting that fast food chain KFC's newly launched set meal that offered limited-edition surprise box gifts had caused irrational and excessive purchases of food.

This sales tactic goes against public order and good custom, and breaches the spirit of the law, the association said.