Background Emergency overcrowding is a serious problem for hospital staff in China. Immigrant patients caused emergency overcrowding in a hospital in southern China. However, the demographic characteristics of this population have not been determined. Methods Data on all emergency visitors, including patients who stayed in emergency department (ED) observation units or critical care units were collected and saved in an Excel sheet. Patient characteristics, including place of origin, type of disease, visiting time, and factors associated with prolonged stay in the ED, were analyzed. Results There were 141,024 emergency visitors in a 5-year interval, and only 24.0% of them were local residents. The number of patients was higher from November to March of next year. Immigrant patients usually had more commodity diseases than local residents. A total of 3,173 patients stayed in the ED observation unit or critical care unit in one-year interval. The number of patients in the ED and their LOS were higher from November 2017 to March 2018. Conclusions Emergency overcrowding in a hospital in southern China was seasonal and was caused by an increasing number of immigrants. Several patients stayed in the ED for a long time, especially those with special commodity diseases. Hospitals and the government should take measures to address the problems related to emergency overcrowding. Key words: Emergency overcrowding; Immigrant patients; Southern China