Mass gatherings can be disruptive to the daily operations of any emergency department (ED). These events usually are spontaneous and sudden. Therefore, operational processes must be effective and concise when dealing with a sudden surge. This study examines the Tan Tock Seng Hospital (TTSH) ED response process to a gastroenteritis (GE) outbreak. Prompt identification and establishment of a casualty holding and treatment area ensured smooth operational capacity, which allowed these patients to be segregated from the mainstream ED crowd and more specific care to be rendered. Entrance and exit points of the designated area were established with controlled access to prevent cross-contamination with the mainstream patient load. Patients with GE who presented with acute symptoms required immediate assessment and intervention, placing stress on existing personnel. Hence, adequate personnel was an important factor that could not be disregarded. Staff burnout was a plausible issue that was recognized from the start and attempts were made to prevent burnout by creating an encouraging work environment and allowing frequent relieving of duties. Communicating the event to relevant departments ensured that the ED was adequately supported during the GE outbreak, both administratively and logistically. This was a reflection of the established communication channels. Leadership also had an essential and crucial role to play as the nursing and medical leaders had to be decisive, delegate roles and give concise instructions during the chaotic situation. The availability and access to ample logistical supplies saves on precious time, which allowed more focus on patients. In summary, procedures and protocols, together with staff preparedness, enhances an ED operational capability of effectively responding to mass gatherings.