China's latest outbreak of the coronavirus in Nanjing has been linked back to a Russian flight, according to the deputy director at the city's centre for disease control and prevention.

Gene sequencing results of 52 cases linked to the outbreak showed they have all contracted the Delta strain, Ding Jie said at a news briefing.

Cases in the early stage of the outbreak were workers at Nanjing Lukou International Airport who cleaned an airplane after it arrived on a flight from Russia, the deputy director said. The gene sequence of the virus found in samples of the workers was identical to that of an infected person arriving from the flight, he said.

Nanjing has reported 13 new domestically transmitted Covid-19 patients for July 29, bringing the total to 184 since July 20, Reuters reports.