Worldwide, norovirus (NoV) is a major cause of acute gastroenteritis (AGE) responsible for pandemics every ~3 years, and over 200,000 deaths per year, with the majority in children from developing countries. In this study, we aimed to investigate the incidence of NoV in children hospitalised with AGE from Belém, Pará, Brazil. We also determined whether viral RNA levels in their blood and faeces correlated with clinical severity. For this purpose, paired stool and serum samples were collected from 445 paediatric patients under 6 years between March 2012 and June 2015. Enzyme-linked immunosorbent assay (EIA) was used to detect NoV and reverse transcription quantitative PCR (RT-qPCR) used to quantify NoV RNA levels. Phylogenetic analysis of sequences from the partial ORF1/2 region (557 bp) was used to genotype the strains detected. NoV antigen was detected in 24.3% (108/445) of stool samples, with viraemia also present in 20.4% (22/108). Viraemia and a high stool viral load (>107 genome copies/gram of faeces) were associated with longer hospitalisations (p=0.0252 and p<0.0001, respectively). The prevalent viruses detected during the study period were the GII.4 variants Sydney 2012 (71.6%, 58/81) and New Orleans 2010 (6.17%, 5/81). In addition, eight other genotypes belonging to GII were detected and four of them were recombinant strains. All sequences obtained from the sera were characterised as GII.4 viruses and shared 100% nucleotide identity with their respective faecal samples. Detection and molecular characterisation of NoV in paired stool and serum samples suggests that the dissemination of NoV to the blood stream is not uncommon, and its occurrence in the blood is related to increased faecal viral loads and disease severity.