The city of around 26 million has seen a record number of asymptomatic cases in recent weeks.
The Shanghai government on Sunday announced they would divide the city into two for testing its millions, using the Huangpu river that passes through the city as a guide
Districts to the east of the river, and some to its west, will be locked down and tested between March 28 and April 1. The remaining areas between April 1 and 5
Although recent case numbers remain insignificant in a global context, they are China's highest since the first weeks of the pandemic, which first emerged in the city of Wuhan in late 2019.
China's National Health Commission on Sunday reported more than 4,500 new domestically transmitted cases, down by more than 1,000 from the previous day
The lockdown means that all firms and factories will suspend manufacturing or work remotely during the lockdown, apart from those involved in offering public services or supplying food.