The COVID-19 cluster in east China's port city of Qingdao originated in two port workers who stayed at the same hospital, the local health commission declared on Friday.

The pair contracted the virus and was put on hospital quarantine in September.

According to authorities, they used a scan room for examination, but the room was not properly disinfected, before receiving other patients on the following day.

Authorities said sequences of the virus' genome of recent cases and the two patients have shown a high level of similarity.

Qingdao firstly reported three asymptotic cases on October 11, and since then 12 confirmed infections were found, all related to a local hospital.

A five-day virus testing program was launched on Monday (October 12), and by Friday morning, over 10.78 million samples had been taken in the city, but no new cases were detected.

The pair, surnamed Chen and Dong, were stevedores of Qingdao Port Dagang Company. They were moved into the hospital for medical observation after testing positive for the novel coronavirus on September 24. They were asymptomatic by then.

They had unloaded imported frozen products on September 19.