A process for the automatic creation of ad-hoc networks between mobile devices in emergency and evacuation events. During an emergency or an evacuation event a command centre (20) issues a special emergency warning to mobile network operators, in response to which the operators broadcast over the mobile network (10) a trigger message to the mobile devices (11-14) that they service. Receipt of the trigger message causes the mobile devices (11-14) in a given geographical area to search for their neighbours and to form groups each having a leader, subsequent communication between the group and the mobile network (10) being conducted via the leader, communications within the group being conducted for example by using Bluetooth or WiFi. In this way, both resources in the mobile network and battery power of the mobile devices are conserved.