China's Wuhan city will test its 12 million residents for the coronavirus after confirming its first domestic cases of the highly transmissible Delta variant.

Wuhan, where the virus first emerged in late 2019, had reported no local coronavirus cases since mid-May last year but on Monday authorities confirmed three cases of the Delta variant. The strain has been found in a handful of provinces and big cities including Beijing over the past two weeks.

"To ensure that everyone in the city is safe, city-wide nucleic acid testing will be quickly launched for all people to fully screen out positive results and asymptomatic infections," Wuhan official Li Qiang told a news briefing.