A Chinese city bordering Myanmar is stepping up efforts to fight a third coronavirus outbreak after several locally transmitted cases were reported this week, AP reports.

Ruili, located in the southwestern province of Yunnan, has initiated mass testing and imposed a lockdown to prevent people from entering or leaving the city unless they can prove their travel is necessary, according to the local government.

More than 230,000 test samples have been collected since Monday, and the Jiegao border community was named a medium-risk area on Tuesday, the wire service quoted China’s Xinhua News Agency as reporting.