The negative impact of loneliness and perceived stress on mental health during two-month lockdown in Shanghai

•Shanghai has experienced the most serious COVID-19 lockdown in 2022 and related studies on mental health were scarce.•There’s an increase in the proportion of lonely people during Shanghai lockdown.•Residents in Shanghai were lonelier and with higher proportion of mental health conditions.•Shanghai lockdown, high loneliness and high perceived stress were associated with poorer mental health.