BEIJING (AP) — China has sent more than 10,000 health workers from around the country to Shanghai, including 2,000 from the military, as it struggles to stamp out a rapidly spreading outbreak in its largest city under its zero-COVID strategy.

Shanghai was conducting a mass testing of its 25 million residents Monday as what was announced as a two-phase lockdown entered its second week. Most of eastern Shanghai, which was supposed to re-open last Friday, remained locked down along with the western half of the city.

While many factories and financial companies have been allowed to keep operating if they isolate their employees, concern was growing about the potential economic impact of an extended lockdown in China’s financial capital, a major shipping and manufacturing center.

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 outbreaks from spreading by isolating everyone who tests positive, whether they have symptoms or not. Shanghai has converted an exhibition hall and other facilities into massive isolation centers where people with mild or no symptoms are housed in a sea of beds separated by temporary partitions.

China on Monday reported more than 13,000 new cases nationwide in the previous 24 hours, of which nearly 12,000 were asymptomatic. About 9,000 of the cases were in Shanghai. The other large outbreak is in northeastern China’s Jilin province, where new cases topped 3,500.

The Shanghai lockdown has sparked numerous complaints, from food shortages to limited staff and facilities at hastily constructed isolation sites. Some people who tested positive have remained at home for extended periods because of a shortage of isolation beds or transportation to take them to a center, the business news publication Caixin said.

Asked about the anxiety of parents separated from their children, Shanghai health commission official Wu Qianyu said Monday that they are required to be kept apart if the child tests positive and the parent tests negative, according to the Paper, an online news outlet.

If both test positive, the parent is allowed to stay with the child at an isolation site for children and receive any treatment there, Wu was quoted as saying at a news conference on Monday.

The China Daily newspaper said nearly 15,000 medical workers from neighboring Jiangsu and Zhejiang provinces left for Shanghai early Monday from their hospitals by bus. More than 2,000 personnel from the army, navy and a joint logistics support force arrived on Sunday, a Chinese military newspaper said.

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

Workers wearing blue protective clothing held up signs saying “Keep one meter distance” and “Do not crowd” as people lined up for testing in one part of western Shanghai. The testing was being done in batches, 10 people at a time. If the sample comes back positive, all 10 are tested individually.

While most shops and other businesses in Shanghai are shut down, major manufacturers including automakers General Motors Co. and Volkswagen AG say their factories are still operating. VW has reduced production because of a disruption in supplies of parts.

Businesses that are operating are enforcing “closed loop” strategies that isolate employees. Thousands of stock traders and other people in financial industries are sleeping in their offices, according to the Daily Economic News newspaper.

Three out of five foreign companies with operations in Shanghai say they have cut this year’s sales forecasts, according to a survey conducted last week by the American Chamber of Commerce in Shanghai and the American Chamber of Commerce in China. One-third of the 120 companies that responded to the survey said they have delayed investments.

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