The need to better monitor coercion practices in psychiatric hospitals has been recognised. We aim to describe how physical restraint events occur in psychiatric hospitals and identify factors associated with physical-restraint use. A cohort register study was used. We analyzed physical restraint documents among 14 wards in two psychiatric hospitals in Hong Kong (1 July and 31 December 2018). In total, 1798 incidents occurred (the rate of physical restraint event 0.43). Typically, physically restrained patients were in early middle-age, of both genders, diagnosed with schizophrenia-spectrum and other psychotic disorders, and admitted voluntarily. Alternate methods for physical restraint were reported, such as an explanation of the situation to the patients, time-out or sedation. A longer period of being physically restrained was associated with being male, aged ≥40 years, having involuntary status, and neurodevelopmental-disorder diagnosis. Our findings support a call for greater action to promote the best practices in managing patient aggression and decreasing the use of physical restraint in psychiatric wards. The reasons for the use of physical restraint, especially for those patients who are admitted to a psychiatric hospital on a voluntary basis and are diagnosed with neurodevelopmental disorders, needs to be better understood and analysed.