The Chinese city of Qingdao is testing its entire population of nine million people for Covid-19 over a period of five days.
The mass testing comes after a dozen cases were found linked back to a hospital treating coronavirus patients arriving from overseas.
In May, China tested the entire city of Wuhan – home to 11 million people and the epicentre of the global pandemic.
The country has largely brought the virus under control.
That’s in stark contrast to other parts of the world where there are still high case numbers and lockdown restrictions of varying severity.
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In a statement posted to Chinese social media site Weibo, Qingdao’s Municipal Health Commission said six new cases and six asymptomatic cases had been discovered.
All the cases were linked to the same hospital, said the Global Times.
The Chinese authorities now have a strategy of mass testing even when a new coronavirus cluster appears to be relatively minor, correspondents said.
The commission added that a citywide testing program had been launched, with five districts to be tested within three days – and the whole city to be tested within five days.
Some 114,862 people – including medical staff and newly hospitalised patients in the city’s hospitals – have already tested negative for the coronavirus, it said.
Videos circulating online showed local residents lining up late on Sunday to get tested, said the Global Times, adding that some of these test points were open from 07:00 to 23:00.
The new cases come a week after China’s Golden Week holiday – which saw millions travel across the country.
A Global Times report quoting the Qingdao Municipal Bureau of Culture and Tourism said the city had received 4.47 million passenger trips over this period.
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The nearby city of Jinan, which is also in the same province as Qingdao, called for anyone who had visited the city since 23 September to get tested for the virus, according to a report by The Paper.
Earlier last month, Qingdao announced that two port workers in the city who handled imported seafood had tested positive for the virus. However, they were not known to have infected anyone else.
Daily coronavirus infections have fallen drastically in China, and for the most part the country appears to have recovered from the worst of the virus.
China currently has 85,578 virus cases and the death toll stands at 4,634.
Earlier this year, China completed a mass testing programme in Wuhan saying 11 million people had been tested in 10 days.
However, the BBC’s Reality Check later estimated that the figure was closer to 9 million over 10 days – still a significant number of people.
Hundreds of testing centres were opened, with thousands of testing staff involved.