Beijing had opened back up recently and had seen the gains it made in improving air quality quickly vanish as vehicular congestion clogged up the city's streets. Now it may see those gains return, after Beijing discovered 79 symptomatic new cases of the coronavirus since Thursday, according to NPR.

All the new cases were traced back to the sprawling Xinfadi wholesale food market on the city's south side. The robust market supplies the city and its surrounding areas with 1,500 tons of seafood, 18,000 tons of vegetables and 20,000 tons of fruit on a daily basis, according to the market's website, as NPR reported.

As The New York Times noted, more than 10,000 people work at the market, which supplies 90 percent of Beijing's fruits and vegetables, according to the state media. The virus was reportedly detected on cutting boards for imported salmon there.

China's state media described its latest effort to curb a potential outbreak in Beijing as a "wartime mechanism." Within that wartime mechanism, authorities swiftly shut down the Xinfadi market, partly or fully closed five others, and locked down 11 nearby residential communities and nine schools in the nearby area. It also started to restrict travel in and out of the city, barring tour groups from other provinces and suspending sporting events, according to official statements and local news, as The New York Times reported. Additionally, across the city, plans for first through third grade students to return to school on Monday were scrapped.

"The risk of the epidemic spreading is very high, so we should take resolute and decisive measures," Xu Hejian, a spokesman for the Beijing city government, said at a press briefing on Monday. On Sunday, he said Beijing had entered "an extraordinary period," as The Guardian reported.

Beijing authorities have a tall order ahead them to initiate contact tracing for people at the market several weeks ago. The first new positive COVID-19 case, which was confirmed on Thursday, came from a man who bought seafood and produce at the market on June 3. He said he did not have any recent travel history, so authorities do not know where he became infected. After he tested positive, two more cases were identified the following day, and the market was sealed off on Saturday morning, according to NPR.

Even though the market was closed, the number of cases continued to rise. In addition to the 79 positive cases, authorities have identified at least 48 asymptomatic cases. Those people are being kept in quarantine.

At the market, Beijing authorities tested nearly 6,000 people working there on Saturday, as well as over 2,300 surfaces. All tested negative. Authorities are also asking everyone who has been in or near the market since May 30 to take a nucleic acid exam, according to NPR.

On Sunday, Beijing ordered all companies to require any employees who have visited the Xinfadi market or had contact with those at the market to quarantine at home for 14 days.

Yang Peng, an epidemiologist with the Beijing city government, told state media the virus resembled the European strain rather than the Wuhan strain, but more investigation was needed, according to The Guardian.

"It is found that the virus came from Europe and the preliminary assessment is that the virus came from overseas. But it is not clear how the virus came into this market," Yang said, according to state media, adding that the virus could have been on contaminated meat or spread from the feces of people at the market, as The Guardian reported.