The Chinese city of Wuhan is drawing up plans to test its entire population of 11 million people for Covid-19, state media report.
The plan appears to be in its early stages, with all districts in Wuhan told to submit details as to how testing could be done within 10 days.
It comes after Wuhan, where the virus first emerged, recorded six new cases over the weekend.
Prior to this, it had seen no new cases at all since 3 April.
Wuhan, which was in strict lockdown for 11 weeks, began re-opening on 8 April.
For a while it seemed like life was getting back to normal as schools re-opened, businesses slowly emerged and public transport resumed operations. But the emergence of a cluster of cases - all from the same residential compound - has now threatened the move back to normalcy.
According to report by The Paper, quoting a widely circulated internal document, every district in the city has been told to draw up a 10-day testing plan by noon on Tuesday.
Each district is responsible for coming up with its own plan based on the size of their population and whether or not there is currently an active outbreak in the district.
The document, which refers to the test plan as the "10-day battle", also says that older people and densely populated communities should be prioritised when it comes to testing.
However several senior health officials quoted by the Global Times newspaper indicated that testing the entire city would be unfeasible and costly.
Peng Zhiyong, director of the intensive care unit of the Zhongnan Hospital of Wuhan University, instead that testing was instead likely to be targeted at medical workers, vulnerable people and those who'd had close contacts with a case.
Another Wuhan University director suggested that a large percentage of Wuhan's population - around 3-5 million - had already been tested, and Wuhan was "capable" of testing the remaining 6-8 million in a 10-days period.
To put the goal into context, the US now conducts around 300,000 tests each day, according to the White House. So far, it's tested almost 9 million people in total.
On Chinese social media site Weibo, people have been raising questions about whether such a large number of tests can be carried out in just a matter of days.
"It is impossible to test so many people," said one commenter, who also questioned how much it would cost.
Another said that such tests should have been carried out before Wuhan re-opened its doors to the rest of China.
Taking no chances
Stephen McDonnell, BBC News, Beijing
Wuhan was where this global emergency started and there was relief when the first cluster site seemed to come out the other side. There would also be despair if the first lockdown city was to be engulfed again by the coronavirus.
Not letting this happen has become a priority for the Chinese government.
When a new domestic infection appeared in the city three days ago you could feel the concern over 1,000km away in Beijing.
Then five others were infected by the 89-year old man previously declared "asymptomatic", and the manager of their housing complex was removed.
However, sacking local officials in this way might also encourage a tendency to hide future cases.
China's most powerful seven people, in the Politburo Standing Committee, met last week to discuss improving the country's early warning system for outbreaks like this.
They could start by easing the "no mistakes at all costs" approach to governing, in which those who reveal the bad news can end up being punished.
China reported just one new cases on Monday, bringing the total number of cases to 82,919, with the death toll at 4,633.
Hundreds of asymptomatic cases are being monitored by Wuhan health authorities