The current two-wave longitudinal study aimed to investigate changes in stress, anxiety, depression, and positive mental health (PMH) during the first COVID-19 pandemic outbreak in the sample of emerging adults. Data were collected before the COVID-19 and within the first month of the outbreak. The study sample consisted of 775 university students from Lithuania ( n = 450, M age( SD age) = 19.45 (0.93), 79.3% female) and Germany ( n = 325, M age( SD age) = 23.08 (2.94), 78.2% female). The results of multivariate Latent Change Analysis revealed that Lithuanian and German emerging adults demonstrated a decrease in stress and anxiety at the COVID-19 outbreak. Lithuanians also showed a decrease in depressive symptoms and an increase in PMH. Three groups with different change patterns were identified: resilient (82%) demonstrating positive changes, high-symptom (8%) with stable high rates of stress and depression and stable low rates of PMH, and vulnerable (10%) with an increase in depressive symptoms as well as a decrease in PMH over time.