Chinese cities have rolled out mass testing of millions of people and imposed fresh travel restrictions as health authorities battled Sunday tto contain the country's most widespread coronavirus outbreak in months.

China reported 75 new coronavirus cases with 53 local transmissions, with a cluster linked to an eastern airport now reported to have spread to over 20 cities and more than a dozen provinces.

The outbreak is geographically the largest to hit China in several months after the country's successes in largely snuffing out the pandemic within its borders last year.

Authorities have now conducted three rounds of testing on Nanjing's 9.2 million residents and placed hundreds of thousands under lockdown, according to an AFP report.