“Meidong firm immediately stopped all operations and shut down the port area after the COVID-19 test of the staff showed positive,” Jiang Yipeng, deputy general manager of Ningbo-Zhoushan port, told Reuters. According to Xinhua, the shutdown will last until “further notice,” while close contacts of the individual have been quarantined and all staff are tested. Xinhua reports authorities have tested 331 people so far and returned zero positive cases.

The shutdown will further strain global shipping lines, which are still recovering from the partial closure of China’s Yantian port in June following reports of an outbreak of 150 COVID cases in a neighboring city. It took a month for operations at Yantian—the world’s fourth-largest port—to return to normal.

According to Reuters, a backlog of 40 container ships were anchored off the coast of Ningbo as of Thursday. Shipping operator CMA CGM said it is rerouting some of its ships to Shanghai, which is about 130 miles north of Ningbo, but Shanghai is already congested.

Ports on China’s east coast, including Ningbo and Shanghai, are still processing a backlog caused by typhoon In-fa in late July. The typhoon depressed container handling 10% across East China ports, according to the China Ports and Harbours Association. The disruptions mounted at the same time as demand from the U.S. increased, with merchants stocking up ahead of holiday sales. Freight costs from China to the U.S. rose to a record $20,000 per 40-foot box last month—a 500% increase on the cost in the same month last year.

Closing an entire terminal for the sake of one COVID case seems heavy-handed but is par for the course for China’s zero-tolerance approach to containing COVID-19. China has survived the pandemic with relatively few outbreaks due to mass testing, instant lockdowns, and closed borders. Yet, for all its precautions, China is currently battling its worst COVID outbreak since the virus emerged in 2019.

China has reported 878 COVID-19 cases in the past two weeks—more than double the total recorded in July. Some 40 cities have reported clusters of the more contagious Delta variant, prompting new lockdowns and citywide COVID-19 testing campaigns.

Last week, authorities ordered all 11.8 million residents of Zhengzhou to undergo mandatory testing, while the city was still recovering from devastating floods that inundated roads and killed over 300 people days earlier.

China has a vaccination rate of around 60%, but some foreign governments have reported Chinese vaccines to have low efficacy against the Delta variant. Analysts say Beijing’s resolute action in suppressing new outbreaks indicates even Beijing doubts the efficacy of China’s homemade vaccines against the Delta variant.

The government has placed particular care in preventing COVID-19 from entering the capital Beijing. In addition to serving as the government’s seat of power in China, Beijing is due to host the Winter Olympics in February next year. Authorities, determined to make the event a success, are planning screening procedures even more stringent than Tokyo deployed during the Summer Olympics this month.

Currently, tourists traveling to the capital from other cities in China are required to present negative COVID tests when entering Beijing and submit to two more weekly tests after arriving. Travel from provinces that have reported COVID outbreaks is strictly forbidden.

On Thursday, the day after a single COVID-19 case was recorded in Ningbo port, local news reported Ningbo airport suspended all flights to the capital citing a “public health incident”—a likely, but unconfirmed, reference to the singular case at the port.