lockdown
noun [ C or U ] mainly US uk/ˈlɒk.daʊn/ us/ˈlɑːk.daʊn/
（建筑或地区）因紧急情况而被封锁了
a situation in which people are not allowed to enter or leave a building or area freely because of an emergency
The Secret Service is imposing a virtual lockdown on the city. 特勤局实质上把整个城市都封锁了。
The school has been placed on lockdown this morning while authorities investigate a bomb threat. 这座学校今天早晨被置于封锁之下，便于当局调查炸弹威胁。