Most low-income and middle-income countries have little or no data integrated into a national surveillance system to identify characteristics or outcomes of COVID-19 hospital admissions and the impact of the COVID-19 pandemic on their national health systems. We aimed to analyse characteristics of patients admitted to hospital with COVID-19 in Brazil, and to examine the impact of COVID-19 on health-care resources and in-hospital mortality. We did a retrospective analysis of all adult patients (age >= 20 years) with quantitative RT-PCR (RT-qPCR)-confirmed COVID-19 who were admitted to hospital between Feb 16 and Aug 15, 2020 (epidemiological weeks 8–33) and registered in SIVEP-Gripe, a nationwide surveillance database in Brazil. We examined the progression of the COVID-19 hospital admissions and inhospital mortality across three 4-week periods within this timeframe (epidemiological weeks 8–12, 19–22, and 27–30) stratified by age, intensive care unit (ICU) admission, and respiratory support for the whole country and its five regions: North, Northeast, Central-West, Southeast, and South. 254 288 patients with RT-qPCR-confirmed COVID-19 were admitted to hospital and registered in SIVEP-Gripe. The mean age of patients was 60 years, 47 per cent were aged younger than 60 years. Case numbers increased across the three 4-week periods studied: by epidemiological weeks 19–22, cases were concentrated in the North, Northeast, and Southeast; by weeks 27–30, cases had spread to the Central-West and South regions. In 232,036 admissions with a defined hospital outcome, the overall in-hospital mortality was 38 per cent, being 59 per cent (47,002 of 79,687) among those admitted to the ICU, and 80 per cent (36,046 of 45,205) among those who were mechanically ventilated. The overall burden of ICU admissions per ICU beds was more pronounced in the North, Southeast, and Northeast, than in the Central-West and South. We observed a widespread distribution of COVID-19 across all regions in Brazil, resulting in a high overall disease burden. In-hospital mortality was high, even in patients younger than 60 years, and worsened by existing regional disparities within the health system. The COVID-19 pandemic highlights the need to improve access to high-quality care for critically ill patients admitted to hospital with COVID-19.