China's Wuhan city will test all of its 12 million residents for the coronavirus, an official said on Tuesday, after the place where the virus emerged in late 2019 confirmed its first domestic cases of the highly transmissible Delta variant.

Wuhan, which gave the world its first glimpses of lockdowns and mass testing, reported no local coronavirus cases since mid-May last year but on Monday, authorities confirmed three new cases of the Delta variant.

"To ensure everyone in the city is safe, city-wide nucleic acid testing...