China is doubling down on its "zero-Covid" strategy, saying the spread of the potentially milder Omicron variant is no reason to lower its guard amid warnings of economic disruptions and even public unrest as lockdowns drag into the third year.

As other countries talk about a transition from "pandemic" to "endemic", China has stepped up policies to stamp out any new outbreak as soon as it arises, sealing off cities, shutting transport links and launching mass testing programmes.

The approach has kept infections at a minimum, but...