Yuan Yang, Nian Liu, Sue-Lin Wong and Qianer Liu:

Three days after the Chinese government locked down Hubei, the province at the centre of the coronavirus outbreak, a local government official more than 1,000km away received data from telecoms carriers alerting her to a list of people who had left Hubei and entered her town.

The data included traces of the estimated locations of users’ mobile phones, showing that many had driven back along the highways from Hubei to Guangdong province in southern China, where the official works in a small town. The location data helped the official’s team “more or less” pin down everyone who came back from Hubei, she said. 

But for another Guangdong town, the information it was able to get hold of was much less comprehensive.

“We did identify one man from Hubei on the list who was high-risk. We searched everywhere for him but just couldn’t track him down,” a second official told the Financial Times, speaking on condition of anonymity.