question: INTRODUCTION: The COVID-19 pandemic caused a healthcare crisis in China and continues to wreak havoc across the world This paper evaluated COVID-19's impact on national and regional healthcare service utilisation and expenditure in China METHODS: Using a big data approach, we collected data from 300 million bank card transactions to measure individual healthcare expenditure and utilisation in mainland China Since the outbreak coincided with the 2020 Chinese Spring Festival holiday, a difference-in-difference (DID) method was employed to compare changes in healthcare utilisation before, during and after the Spring Festival in 2020 and 2019 We also tracked healthcare utilisation before, during and after the outbreak RESULTS: Healthcare utilisation declined overall, especially during the post-festival period in 2020 Total healthcare expenditure and utilisation declined by 37 8% and 40 8%, respectively, while per capita expenditure increased by 3 3% In a subgroup analysis, we found that the outbreak had a greater impact on healthcare utilisation in cities at higher risk of COVID-19, with stricter lockdown measures and those located in the western region The DID results suggest that, compared with low-risk cities, the pandemic induced a 14 8%, 26 4% and 27 5% reduction in total healthcare expenditure in medium-risk and high-risk cities, and in cities located in Hubei province during the post-festival period in 2020 relative to 2019, an 8 6%, 15 9% and 24 4% reduction in utilisation services;and a 7 3% and 18 4% reduction in per capita expenditure in medium-risk and high-risk cities, respectively By the last week of April 2020, as the outbreak came under control, healthcare utilisation gradually recovered, but only to 79 9%-89 3% of its pre-outbreak levels CONCLUSION: The COVID-19 pandemic had a significantly negative effect on healthcare utilisation in China, evident by a dramatic decline in healthcare expenditure While the utilisation level has gradually increased post-outbreak, it has yet to return to normal levels