Introduction The potential role of medical students in raising awareness during public health emergencies has been acknowledged. To further explore their potentials as public educators and role models for the communities during the coronavirus disease 2019 (COVID-19) pandemic, this study aims to assess the knowledge, attitude, and practice of these students toward COVID-19. Methods An online cross-sectional survey was conducted among undergraduate medical students in Indonesia. Socio-demographics characteristics, social interaction history, information-seeking behavior, as well as knowledge, attitude, and practice toward COVID-19 were collected through a self-reported questionnaire. A p-value of <0.05 indicated statistical significance. Results Out of 4870 respondents, 64.9% had positive attitude and 51.5% had positive practice toward COVID-19, while only 29.8% had adequate knowledge. Knowledge was slightly positively correlated with attitude and practice (ρ = 0.074 and ρ = 0.054, respectively; both p<0.001), while attitude was weakly correlated with practice (ρ = 0.234, p<0.001). Several factors including age, sex, place of residence, institution type, academic level, family income, history of chronic illness, prior volunteering experience, and perceptual awareness on COVID-19 were significantly associated with either knowledge, attitude, and/or practice toward COVID-19. Furthermore, health institution's and the government's press releases, as well as health expert opinions were deemed as the most reliable sources of COVID-19-related information-yet trivially none of these sources were associated with knowledge, attitude, and practice in the study population. Conclusion Many undergraduate medical students in Indonesia had positive attitude and practice against COVID-19, yet only a few had adequate knowledge. This warrants further interventions to keep them updated with COVID-19 evidence to maximize their potentials in raising public awareness on COVID-19.