question: OBJECTIVES: This study aimed to examine the prevalence of peritraumatic stress symptoms (PTSSs), perceived threat, social support and factors contributing to clinically significant PTSS among frontline COVID-19 healthcare workers (HCWs) in China. DESIGN AND SETTING: An online survey through self-administered questionnaires was conducted from 18 February to 4 March 2020, during the outbreak of COVID-19. OUTCOMES MEASURES: PTSS was assessed using the post-traumatic stress disorder (PTSD) self-rating scale. Demographic and socioeconomic characteristics, self-reported health, physical/psychological symptoms, perceived threat from frontline work and perceived social support were investigated. Multivariable line regression analysis distinguished factors associated with HCWs’ PTSS scores. RESULTS: A total of 676 (58.1%) HCWs have shown clinically significant high levels of PTSS. Only 441 (37.9%) self-reported good health. Most had physical symptom(s) (915 (78.7%)), psychological symptom(s) (906 (77.9%)), inability to vent emotions (284 (24.4%)), emotional exhaustion (666 (57.3%)) and 1037 (89.2%) needed professional respect. Moreover, social support received was less than expected, and the receipt of psychological services/help scored the lowest (3.11±1.73). Combined psychological and physical symptoms, difficulty in releasing tension and venting emotions timely, fear of infection, emotional exhaustion and depersonalisation are significantly associated with PTSS scores among frontline HCWs. Working ≥8 hours, having the senior professional title, self-reported health, enjoying perfect protection and control measures, economic subsidy and control policy on reducing discriminatory practices are negatively correlated with PTSS scores. CONCLUSIONS: During the outbreak of COVID-19, frontline HCWs experienced clinically significant high levels of PTSS and heavy workload, and the emergency resulted in their inadequate psychosocial support. If this is left unchecked, HCWs have a higher risk of developing PTSD. Early detection, identification and person-directed, targeted multidisciplinary interventions should be undertaken to address various influencing factors. Comprehensive measures, including setting up emotional release channels, as well as providing psychological and social support intervention for HCWs globally, are highly recommended.