China has sent more than 10,000 health workers from across the country to Shanghai, including 2,000 from the military, as it struggles to contain the fast-spreading outbreak under a zero-COVID strategy in its largest city.

Shanghai conducted mass testing of its 25 million residents on Monday as the announced two-phase lockdown entered its second week. Much of eastern Shanghai, which was due to reopen on Friday, remains on lockdown along with the western half of the city.

While many factories and financial firms have been allowed to continue operating while quarantining their employees, concerns have grown about the possible economic fallout from a prolonged lockdown in China’s financial capital, a major shipping and manufacturing hub.

The highly contagious omicron BA.2 form of the virus is testing China’s ability to maintain its zero-COVID approach, which aims to stop the spread of the outbreak by isolating all people who test positive, whether they have symptoms or not. Shanghai has transformed an exhibition hall and other facilities into a large isolation center, housing mild or asymptomatic people in a large number of beds separated by temporary partitions.

China on Monday reported more than 13,000 new cases across the country in the past 24 hours, nearly 12,000 of whom were asymptomatic. About 9,000 of them are in Shanghai. Another large outbreak was in northeastern China’s Jilin province, where more than 3,500 new cases were reported.

The lockdown in Shanghai has sparked complaints ranging from food shortages to hastily built quarantine sites with limited personnel and facilities. Caixin, a business news publication, said some people who tested positive were staying at home for long periods of time due to a lack of isolation beds or transportation to get them to the center.

When asked about the anxiety of parents being separated from their children, Wu Qianyu, an official with the Shanghai Municipal Health Commission, said on Monday that if a child tests positive and a parent tests negative, they must be isolated, according to the online news outlet The Paper.

Parents are allowed to stay with their children at the child isolation site and receive any treatment there, if both test positive, Wu said at a news conference on Monday.

Nearly 15,000 medical workers from neighboring Jiangsu and Zhejiang provinces took a bus from the hospital to Shanghai early Monday, the China Daily said. More than 2,000 personnel from the army, navy and joint logistics support force arrived on Sunday, Chinese military newspapers said.

At least four other provinces have also sent doctors, nurses and other medical personnel to Shanghai, the state-owned China Daily said.

In one location in western Shanghai, workers in blue protective suits held signs that read “Keep a metre apart” and “Don’t crowd” as people queued for testing. The tests are conducted in batches of 10 people at a time. If the sample returns positive, all 10 samples are tested individually.

While most stores and other businesses in Shanghai were closed, major manufacturers including automakers General Motors Co and Volkswagen AG said their factories were still operating. Volkswagen has cut production due to disruptions in parts supply.

Businesses that are operating are implementing a “closed loop” strategy of isolating employees. According to the Daily Economic News, thousands of stock traders and others in the financial industry are sleeping in their offices.

Three-fifths of foreign companies doing business in Shanghai said they had lowered their sales forecasts for this year, according to a survey last week by the American Chamber of Commerce in Shanghai and the American Chamber of Commerce in China. A third of the 120 companies that responded to the survey said they had delayed investing.

Shanghai has set up temporary vegetable warehouses to boost supply, and an online grocery delivery service has doubled staff at one of the warehouses to keep up with demand, the official Xinhua news agency said. City officials have apologized for the government’s handling of the lockdown.