Taiwan reported its first domestically transmitted case of the highly contagious Delta variant of Covid-19 on Saturday, tightening controls in a southern part of the island where the cases have occurred.

Taiwan is battling a cluster of domestic infections, almost all of them due to the previously globally dominant Alpha variant, though numbers are steadying and the outbreak has been comparatively small.

Six people in Pingtung county had been confirmed to have the Delta variant, including two who...