A new coronavirus emerged in December 2019 and quickly spread globally, causing unprecedented social, psychological, and economic damage. This study aimed to investigate people’s emotional reactions to the COVID-19 pandemic. The dataset for this study consisted of 2,013 adults (962 males and 1,053 females) in four countries (Italy, Lebanon, Portugal, and Serbia). A snowball sampling technique that focused on recruiting the general public living in countries during the COVID-19 epidemic was utilized. An online survey was disseminated at the same time, in March–April 2020, when many countries were exposed to COVID-19. Results indicated that, with regard to gender, females had more psychological reactions to COVID-19 than did males. People who had one child were more stressed than people with no children. Extensive knowledge of COVID-19 was found to trigger more anxiety. Results showed that stress and overall emotional reactions increased with age. The findings can be used to develop psychological interventions to improve mental health and psychological resilience during the COVID-19 epidemic. Keywords: pandemic; stress; anxiety; depression; adult, COVID-19; emotion; disaster; disease.