Nearly 9,000 nucleic acid sample collection sites have been set up across Shanghai to serve the increasing number of employees returning to work as the city's pandemic gradually wanes.

More than half of the PCR testing sites have opened, mainly for workers maintaining urban services, companies resuming operations and citizens in precautionary areas, the city's reform and development commission said.

Citizens can check their nearest PCR sample collection sites on the Suishenban app and WeChat app, along with information such as how many people are waiting, said Chen Shiyan, deputy director of the commission.

As the city's COVID-19 infections keep trending downwards, over 70 percent of Shanghai's over 1,800 key companies have resumed operations, said Zhang Hongtao, chief engineer of Shanghai Commission of Economy and Informatization.

Over 90 percent of the first batch of some 660 key companies, especially in the automotive, integrated circuit and bio-medicine sectors, have maintained stable production, Zhang told the city's daily COVID-19 press briefing.

He noted some subdistricts, towns or industrial parks have been found to be stepping up the standards in the name of COVID-19 prevention and control. He asked them to follow the unified standard of the city government.

"It is unnecessary and shouldn't set additional thresholds for companies who want to restore operations," Zhang said.

Shanghai has released an updated work resumption guideline, which stipulates all returning personnel and new hires have to take two tests each day – an antigen test in the morning and a nucleic acid test in the afternoon.

Companies in locked down areas should organize all employees to take two tests each day, including an antigen test in the morning and a nucleic acid test in the afternoon.

Those in controlled areas should arrange an antigen test each day and a nucleic acid test every two days, while those in precautionary areas should have an antigen test each day and a nucleic acid test within five days.

Companies are asked to categorize their production areas in four tiers, according to the risk level, in the colors of green (protection zone), blue (observation zone), yellow (quarantine zone) and red (infection zone).