Authorities in the Chinese metropolis of Qingdao believe the coronavirus could spread locally through two dockers.
Due to the outbreak in the eastern coastal city, the government is having all nine million inhabitants tested in a few days. That operation must be completed on Friday.
Thirteen new corona infections came to light in the city this week. In most cases, these could be linked to a hospital. There, the infected dockers would have undergone a medical check and spread the virus.
According to a health official, insufficient measures had been taken to prevent this.
Authorities in the city found the coronavirus on the packaging of imported food last month. This happened after two employees of an import company had tested positive. It is unclear whether it concerns the two dockers.
It is not the first time that an entire city has been tested in China. This already happened in Wuhan, where the virus first appeared. People have also been tested on a large scale in the capital Beijing.
China, with 1.3 billion inhabitants, reported a total of more than 90,000 infections, according to figures from the American Johns Hopkins University.