Shanghai will start the second phase of its lockdown on Friday and begin mass testing of more than 16 million residents living in Puxi, the area west of the Huangpu River.

Two rounds of nucleic acid tests were due to have been completed by 3 am on Friday among around 9.1 million residents east of the Huangpu River, who have been under lockdown since Monday.

Communities east of the Huangpu River will be categorized into grids by level of exposure risk to the COVID-19 based on the test results and through consultation with the expert team from the central government, and each grid will observe according epidemic control protocol starting at 5 am, Friday, said the municipal government in a statement on Thursday night.

"The testing conducted in the Puxi area will involve more people and cover 12 districts, making it a more complicated situation," said Ma Chunlei, secretary-general of Shanghai municipal government. "We have formed six task forces to handle problems related to the construction of new quarantine facilities, ensuring the supply of resources and addressing urgent demand from residents."

Shanghai is currently experiencing its worst COVID-19 outbreak in two years, with more than 30,000 new infections reported since the beginning of March. The city reported 5,653 new cases on Wednesday, 5,298 of which were asymptomatic.

At a meeting on Wednesday night on the city's epidemic control efforts, Li Qiang, the city's Party secretary, called on the thousands of government officials working in Shanghai to ensure that all residents are tested within the stipulated time frame.

"We must win this difficult war, and the only way to victory is through perseverance," Li said. "We are at the most difficult stage of the battle, and every minute counts. As long as we are united, there's no hardship we cannot overcome."

Li also stressed that officials at all levels should gather all resources available and go all out to solve problems and issues which are either essential or supportive of epidemic control and prevention, such as lockdown management, test management, epidemiological tracing, disinfection, construction and management of quarantine facilities, as well as ensuring food supply and medical services and other related work at the community level.

"This work should be done seamlessly, so we can have the exposure risk to the virus under control," said Li, adding that the city should achieve zero infections as soon as possible.

At Thursday's news conference, Ma also apologized for the inconvenience caused by the lockdown, and said that the local government had underestimated the spread of the Omicron variant, had not made enough preparations for the surge in new infections, and caused difficulties for residents in locked-down areas.

"We accept the criticisms sincerely and are working on improvements," said Ma.

Wu Jinglei, director of the city's health commission, said it has worked to enhance the deployment of resources, including both medical equipment and personnel, to treat patients who need kidney dialysis services.

The city has also increased the number of its available ambulances by 50 percent to meet the surging demand for emergency services, Wu said.

The neighboring provinces of Jiangsu and Zhejiang have sent teams of more than 2,000 medical workers to support Shanghai's mass testing since Monday. The city has also received tons of food and other daily necessities from across the country.

"We thank all the friends who helped and supported Shanghai, and express our sincere gratitude to all Shanghai residents for their understanding and cooperation," Ma said.