cordon something off
phrasal verb with cordon verb uk/ˈkɔː.dən/ us/ˈkɔːr.dən/
设置警戒线将…围起，封锁
If people in authority, such as the police, cordon off a building or area, they put something around it in order to stop people from entering it.
They've cordoned off the whole area because of a suspected bomb. 因怀疑有炸弹，他们封锁了整个地区。