AP PHOTOS: A first-person view inside Beijing's virus tests

BEIJING (AP) — As the number of COVID-19 cases climbed in Beijing in recent days, officials identified more than 350,000 people who needed to be tested.

I was one of them.

After word first emerged of a cluster of cases at a sprawling wholesale market in the Chinese capital, I had gone to the area to take photographs. Although I never entered the Xinfadi market and only took photos from nearby streets, unknown to me, I had been flagged as a potential vector for the virus.

My phone rang on Wednesday afternoon. An official from my neighborhood’s community association informed me that I should shortly report to the gates of a nearby sports stadium to be bused to a coronavirus testing site.

The caller did not know my name, but they knew that someone associated with my cellphone number had been in the vicinity of the market. I may have been tracked through my cellphone. A Beijing city official said Wednesday that 355,000 people have been identifed for testing via big data, but he did not specify how.

Several dozen people milled about at the meeting point, eyeing each other suspiciously and staying apart. A few wore multiple face masks on top of each other. After checking in, we were escorted to buses — one person per row.

The buses took us to a large city park, where the grounds of a museum had been converted into a temporary testing site. Hundreds of people were already in line. Many said that, like me, they had not visited the market but just been in the area. Some complained that they had merely driven past on a highway.

An official with a loudspeaker ordered people to spread out, but the size of the crowd and the length of the line led to people inching together.

I looked around with some worry — was I standing among Xinfadi workers or daily customers? I had...