The announcement broke a two-month streak with no virus transmissions reported within China, though China has a practice of not reporting asymptomatic cases.
The ruling Communist Party has lifted most curbs on travel and business but still monitors travellers and visitors to public buildings for signs of infection.
Authorities were investigating the source of the infections found in eight patients at Qingdao’s Municipal Chest Hospital and one family member, the country’s National Health Commission (NHC) said.
“The whole city will be tested within five days,” the NHC said on its social media account.
China, where the pandemic began in December, has reported 4,634 deaths and 85,578 cases, plus nine suspected cases that have yet to be confirmed.
The last reported virus transmissions within China were four patients found on August 15 in the north-western city of Urumqi in the Xinjiang region. All the cases reported since then were in travellers from outside the mainland.
The ruling party lifted measures in April that cut off most access to cities with a total of some 60 million people including Wuhan in central China.
Qingdao is a busy port and headquarters for companies including Haier, a major appliance maker, and the Tsingtao brewery. The government gave no indication whether the latest cases had contact with travel or trade.
Travellers arriving from abroad in China still are required to undergo a 14-day quarantine.
