AIM: To investigate the sleep quality and its influencing factors among nurses in hospitals in Zhejiang, China, during the first explosive COVID-19 outbreak following the relaxation of prevention and control measures. DESIGN: A multicentre cross-sectional study. METHODS: Between 10 January and 20 January 2023-approximately 1 month after the policy was loosened-a total of 573 nurses from tertiary and community hospitals in Zhejiang participated in an online, self-administered survey. The participants were recruited using convenience sampling, and the survey was distributed via the WeChat platform. The survey included a general information form; the Self-Rating Scale of Sleep (SRSS); the Depression, Anxiety, and Stress Scale-21 (DASS-21); the Perceived Social Support Scale (PSSS); and the Brief Resilience Scale (BRS). Data analysis was conducted using SPSS version 26.0. Statistical methods employed included t-tests, one-way analysis of variance (ANOVA), chi-square tests and Mann-Whitney U-tests for comparisons between groups. Pearson correlation coefficients were calculated to analyse the relationship between the SRSS score and the DASS-21, PSSS and BRS scores. A multiple linear stepwise regression analysis was conducted to determine the independent influencing factors of sleep quality. RESULTS: More than 90% of the nurses were infected with COVID-19, and 60.6% had sleep disorders. The regression analysis revealed that anxiety, the BRS score, comorbidities, hospital grade, clinical front-line, age and COVID-19 infection independently predicted sleep quality. The scores for several SRSS items were higher than the Chinese norm, especially for the nurses in tertiary hospitals. PATIENT AND PUBLIC CONTRIBUTION: No patient or public contribution.