This photo captures people walking towards Terminal 1 of Nanjing Lukou International Airport in Nanjing, east China's Jiangsu province, on July 29, 2020. (JI CHUNPENG / XINHUA)

NANJING - Nanjing will launch mass coronavirus tests for all its 9.3 million residents soon after nine locally transmitted cases and five asymptomatic cases were reported as of Wednesday afternoon.

Hu Wanjin, a vice-mayor of Nanjing, said at a news conference that three other samples collected from staff members at the city's Lukou International Airport — which came back positive for COVID-19 — still needed further diagnosis before being announced as confirmed cases.

"All 17 people who tested positive for the virus work as cleaning staff at the airport," he said. "As of 5 am Wednesday, 157 contacts have been traced, and more remained to be found."

Testing of residents living in Jiangning district, where the airport is situated, will be completed on Wednesday, he added.

Over 65 percent of flights at Nanjing Lukou International Airport were canceled following the positive COVID-19 cases

Local health authorities detected the positive results during routine nucleic acid testing for airport staff.

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Over 65 percent of flights at the airport were canceled as a result. The airport was earlier scheduled to handle 405 inbound and outbound flights on Tuesday.

The airport has carried out disinfection work inside terminal 2, which mainly handles international operations.

Jiangning, which has a population of more than 1.9 million, upgraded four communities and villages from low-risk to medium-risk for COVID-19 on Wednesday morning and quarantined the Lukou community to contain the virus.

With the risk level upgrade, Nanjing has suggested that people not leave the city. Anyone who has to leave the city must present a negative nucleic acid test result taken within 48 hours since Wednesday.

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The city's education bureau has notified after-school tutoring groups to suspend classes.

Nanjing Drum Tower Hospital, one of the city's top hospitals, has suspended outpatient services to help contain the virus.

Nanjing has formed a medical team of more than 1,500 people to trace the source of the virus. It is possible that the cleaning workers were infected by imported cases at the airport, officials said at the news conference.

With Xinhua inputs