Authorities in China's Wuhan said they would test the city's population for Covid-19, as the virus returned to the place where it first emerged.

China had brought domestic cases down to almost zero, allowing the economy to rebound and life to return largely to normal.

But a fresh outbreak has thrown that record into jeopardy, as the fast-spreading Delta variant reaches dozens of cities after infections among airport cleaners in Nanjing sparked a chain of cases.

In Wuhan -- where the virus first emerged in December 2019 and which faced a lockdown in the early months of the pandemic -- authorities said they were launching a mass-testing programme for all 11 million residents.

And across China, authorities have confined the residents of entire cities to their homes, cut domestic transport links and started mass testing in recent days as the country battles its largest coronavirus outbreak in months.