Chinese cities rolled out mass testing of millions of people and imposed fresh travel restrictions as health authorities battled on August 1 to contain the country's most widespread coronavirus outbreak in months.

China on August 1 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.

That record has been thrown into jeopardy after the fast-spreading Delta variant broke out at Nanjing airport in eastern Jiangsu province in July.

Authorities have now conducted three rounds of testing on the city's 9.2 million residents and placed hundreds of thousands under lockdown, in an effort to curb an outbreak Beijing has blamed on the highly-contagious Delta variant and the peak tourist season.

Officials are now scrambling to track people nationwide who recently travelled from Nanjing or Zhangjiajie, a tourist city in Hunan province which has locked down all 1.5 million residents and shut all tourist attractions.

More than 1.6 billion vaccine doses have so far been administered nationwide as of July 30, Beijing's National Health Commission (NHC) said. It does not provide figures on how many people have been fully vaccinated.