Chinese cities have rolled out mass testing of millions of people and imposed fresh travel restrictions as health authorities battle to contain the country’s most widespread coronavirus outbreak in months. China on Sunday 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.