Background: The sudden emergence of the novel and severe 2019 Coronavirus disease (COVID-19) would be expected to impact the mental health of healthcare workers and thus represent a challenge to psychological resilience. In order to reduce psychological impacts, more research data are needed to help develop evidence-based strategies. We conducted a single center, cross-sectional study, with the aim of assessing the immediate psychological impact of COVID-19 pandemic on medical and paramedical staff in a cancer treatment center providing continuous health care during the pandemic. Methods: From April 19th to May 5th, 2020, medical and nursing staff from Oncology and Hematology Center of Mohammed VI University Teaching Hospital was invited to participate with a self-report questionnaire. We used Impact of Event Scale-Revised (IES-R), Hospital Anxiety and Depression scale (HADS), and Insomnia Severity Index (ISI) to evaluate stress, anxiety, depression, and insomnia, respectively. Additional information on demographic characteristics, medical history, exposure to COVID-19, and accessed mental health services were included in the questionnaire. Results: We received 93 completed questionnaires. Among all healthcare workers included in this study, 30.1% reported stress, 32.3% had anxiety, 30.1% reported depression, and 31.2% had insomnia symptoms. Occupation, female gender, concomitant chronic diseases, history of mental disorders, and history of contact with suspected or confirmed patients were risk factors for psychological disturbances, whereas care provided by hospital decision-makers, and full coverage of all departments with protective measures were protective factors. Conclusion: During the initial phase of COVID-19 outbreak in Morocco, about one-third of the respondents reported moderate to severe psychological impact, and more than half rated their anxiety, depression symptoms, and insomnia as moderate to severe. Our findings emphasize the importance ...........