China on Monday locked down a county that has seen the most COVID-19 cases in the country’s latest delta outbreak, as an initial flareup in the northwest quickly spirals into a nationwide surge.

Ejin, a county in northwestern China’s Inner Mongolia, has asked its 35,700 residents to stay home from Monday and warned of civil and criminal liabilities should anyone disobey the order, state broadcaster CCTV reported, citing a local government statement. The small county bordering Mongolia is the current outbreak’s hotspot, home to nearly one-third of the more than 150 infections found over the past week in the mainland.

The lockdown came a day after a warning from National Health Commission officials that the outbreak would continue to worsen after spreading to 11 provinces in about a week. China reported 38 COVID-19 infections on Monday, half of which were found in Inner Mongolia.