A fire in a residential high-rise in Urumqi, where many residents have been under lockdown, set off public anger and questions about China’s zero-Covid policy.

Hundreds of workers are said to have fled, afraid of being forced into quarantine with inadequate food and supplies.

An outbreak in Zhengzhou has sent an unknown number of workers at the city’s Foxconn plant into quarantine. It’s a bad time of year for...