BACKGROUND: Nurses are experiencing tremendous stress during the new coronavirus disease 2019 (COVID-19) pandemic, especially intensive care nurses. The pandemic of the disease is a tragedy, which may leave a catastrophic psychological imprint on nurses. Understanding nurses' mental distress can help when implementing interventions to mitigate psychological injuries to nurses. AIMS AND OBJECTIVES: To quantify the severity of nurses' post-traumatic stress disorder (PTSD) symptoms and stress and explore the influencing factors of their psychological health when caring for patients with COVID-19. DESIGN: A cross-sectional survey. METHODS: The PTSD Checklist-Civilian and the Perceived Stress Scale were administered from 11 to 18 March 2020, to 90 nurses selected from another city to go and help an intensive care unit (ICU) in Wuhan, China. These nurses were selected because of their high levels of clinical performance and resilience status. RESULTS: Nurses' average PTSD score was 24.62 ± 6.68, and five (5.6%) of the nurses reported a clinically significant level of PTSD symptoms (>38 points). Nurses' perceived stress averaged 19.33 ± 7, and 20 nurses (22.22%) scored positively >25 points. Nurses' stress and PTSD symptoms were positively correlated (P < .01). Major stress sources included working in an isolated environment, concerns about personal protective equipment shortage and usage, physical and emotional exhaustion, intensive workload, fear of being infected, and insufficient work experiences with COVID-19. CONCLUSIONS: This study showed that even relatively highly resilient nurses experienced some degree of mental distress, including PTSD symptoms and perceived stress. Our findings highlight the importance of helping nurses cultivate resilience and reduce stress. RELEVANCE TO CLINICAL PRACTICE: Recommendations for practice include providing adequate training and orientation before assigning nurses to ICU to help, offering disaster-emergency-preparedness training to keep nurses prepared, providing caring and authentic nursing leadership, offering ongoing psychological support to frontline nurses.