Since the end of March, China’s largest city, Shanghai, announced the beginning of large-scale quarantine restrictions to contain the COVID-19 outbreak, and only last week the city authorities announced a list of 666 companies that will be given priority to resume work, CNBC writes.

On the one hand, such a move by the authorities could not but please foreign companies, which said that compiling such a list was a step in the right direction, but on the other hand, the quarantine restrictions keep more than half of the workers at home, preventing them from going to work in factories.

Since late March, mainland China has imposed travel restrictions and bans in the country’s economic centers, ranging from the southern city of Shenzhen to the northern province of Jilin. The degree of disease control varies by region.

The quarantine in the country’s southeastern metropolis of Shanghai has been one of the most disruptive, both to daily life and to foreign businesses and their supply chains. The city accounts for a very small share of China’s GVC – about 3.8 percent – but is home to the world’s busiest port.

Last Friday, China’s Ministry of Industry and Information Technology called for prioritizing the reopening of 666 large enterprises in industries such as biopharmaceuticals, automobiles and machinery, and chemicals.

However, even the compilation of such a list has done nothing to help factories resume their previous productivity: many companies still face labor shortages and logistical difficulties, as less than 30 percent of employees are eligible to return to work.

Being on this list means that a plant can resume operations, but only if workers live on a production site adjacent to it and their contacts are limited to people who have actually tested negative for the virus. Companies cannot easily hire new employees for other shifts.

Before the list was published, some companies in Shanghai and other quarantined regions were able to maintain minimal closed-loop operations.

When companies try to resume production and hire new workers, they usually fail because of the regions’ refusal to let locals go to work.

Closely adjoining this is another problem – the travel restrictions of people working in factories who are allowed to leave their apartments. Transportation restrictions can also affect the delivery of parts for production. With restrictions in place, truck drivers fear that if they venture into the plant, they will find themselves under a 14-day quarantine and possibly miss delivery deadlines.

Though even being utilized at only 30% capacity for a week or so is not a bad result for business.

Quarantine restrictions in China vary from province to province and can include both a complete travel ban and requirements to test drivers for the virus. Drivers are required to wait for negative test results before moving on.

The various measures have already caused uneven damage to businesses, whether foreign or Chinese in the country. From April 1 to April 17, road freight traffic in China fell 27.2 percent year-on-year, while in Shanghai, the transportation index fell 82.6 percent over the same time period.

For a number of companies, this creates a particularly worrying situation: if work and production in Shanghai does not resume by May, all industrial and technology companies in China with supply chain links to the region will have to halt production, especially of automobiles.

Manufacturers can only hope that the national government realizes how important Shanghai is. “On the other hand, 600 manufacturing companies is a good first step, but there are thousands of manufacturing companies in Shanghai that are still closed,” as Michael Hart, president of the American Chamber of Commerce in China, was quoted as saying in Beijing.

Shanghai is still reporting about 20,000 new daily COVID-19 cases, both with and without symptoms of infection.