Customers shop in a Costco warehouse store in Minhang District, east China's Shanghai, Sept. 19, 2019. U.S. retail giant Costco Wholesale openend its first brick-and-mortar store on the Chinese mainland in late August. The store has been running for three weeks and customer passions remain unabated, with short-time queuing still required to enter the store. (Xinhua/Liu Ying)

US supermarket giant Costco moved to restrict daily flow ceiling of shoppers to 2,000 people at its Shanghai outlet and required consumers to wear face masks all the time within the supermarket, according to a Costco notice on Sunday.

The new measure came after the supermarket received an oral warning from Shanghai's Minhang district government after large crowds of shoppers were found gathering at the store on Saturday. 

A working group consisting of local police, the market regulation department, and health and disease control departments are expected to conduct onsite inspections on Sunday to check security loopholes there, domestic media outlet thepaper.cn reported.

There were long queues in the fresh food area in the supermarket and it would take as long as two hours to reach the goods, Shanghai's local media reported.

Chinese netizens expressed concerns on Chinese Twitter-like Weibo platform, saying the novel coronavirus-caused epidemic has not yet been constrained and it is too early to loosen vigilance at the moment when the country's new confirmed coronavirus cases are still rising, although the cases outside the epicenter of Central China's Hubei Province have shown signs of dropping.

A netizen said: "Please do not let down the people who are going giving their all to save patients and fight the battle at the cost of their lives."

Official data showed 648 new cases of coronavirus infections, 97 new deaths were reported on Saturday in the Chinese mainland. As of press time on Sunday, the total infection soared to 77,041, with 2,445 deaths.

Costco, which has a members-only customer base, has continued normal operation during the outbreak of the coronavirus and adjusted its trading hours to 9 am to 7 pm since February 5. 

Costco's Shanghai store was forced to close early on its opening day last August after causing a Black Friday-like sensation. It then put a cap on the number of shoppers allowed in the store to 2,000 from the second day of its opening.

It is planning to open the second outlet in Shanghai's Pudong New Area, but the timetable for construction and operation has not been nailed down, thepaper.cn reported. 

Prior to the first brick-and-motor store in China, Costco has had an online presence in China for five years through a partnership with Chinese tech giant Alibaba Group.