noun
cordon; police line; barricade
A line or barrier set up by police or authorities to restrict access, often at crime scenes, accidents, or emergencies.
警察は事故現場に非常線を張った。
The police set up a cordon around the accident site.
非常線の内側には入れません。
You cannot go inside the police line.
Compound of 非常 (emergency) and 線 (line), literally 'emergency line'.