The Chinese city of Wuhan, where the coronavirus was first detected last year, has identified just 300 cases of the disease following a huge drive to test all 10 million residents, according to officials.
During the 19-day testing program, the city found no infections among 1,174 close contacts of positive cases, suggesting they were not spreading it easily to others.
The new data jars with widespread concern that infected people without symptoms could be silent spreaders of the disease.
There is no definitive answer yet on the level of risk posed by asymptomatic cases, with anecdotal evidence and studies to date producing conflicting answers.
"It not only makes the people of Wuhan feel at ease, it also increases people's confidence in all of China," Feng Zijian, vice director of China's Center for Disease Control and Prevention, told state broadcaster CCTV.
Wuhan was by far the hardest hit city in China, accounting for more than 80 per cent of the country's deaths, according to government figures.
A city official announced Tuesday that the city completed 9.9 million tests from May 14 to June 1.
If those tested previously are included, virtually everyone above the age of 5 in the city of 11 million people has been tested, said Li Lanjuan, a member of a National Health Commission expert team.
"The city of Wuhan is safe," she said at a news conference with city officials.
The campaign was launched after a small cluster of cases was found in a residential compound, sparking concern about a possible second wave of infections as Wuhan emerged from a 2 1/2 month lockdown.
The industrial city on the Yangtze River in central China spent 900 million yuan (about £99.3 million) on the tests, the official Xinhua News Agency said, citing a Wuhan official
The rapid testing of so many people was made possible in part through batch testing, in which samples from up to five people are mixed together, Xinhua reported.
If the result is positive, then the people are individually tested.
National resources were also mobilized to help, said Wang Weihua, deputy director of the Wuhan Health Commission, according to Xinhua.
Together, these efforts raised Wuhan's daily testing capacity from 300,000 to more than one million, she was quoted as saying.