The wireless sensor network (WSN) is one of the most promising technologies which helps making our society safe, secure, and comfortable. A WSN as a social infrastructure must transmit critical information faster and more reliable than other information. In this paper, we propose an autonomous and distributed mechanism, called an “assured corridor” mechanism (ACM), for fast and reliable transmission for urgent information in WSNs. In ACM, a self-organizing corridor consists of nodes surrounding the path from the source node to the base station and nodes in the path. The former refrains from transmitting non-urgent information to avoid collisions with emergency packets, and the latter suspends their sleep schedule and keeps awake to avoid delay caused by sleeping. We conducted simulation experiments with a tree-based and broadcast-based network. It was shown that ACM improved the delivery ratio and the delay of emergency packets.