This study reports the isolation and characterization of 61 SARS-CoV-2-neutralizing monoclonal antibodies from five patients with severe COVID-19. Among these, 19 antibodies showed potent neutralization of authentic SARS-CoV-2 in vitro, with nine exhibiting very high potency (50% virus-inhibitory concentrations of 0.7 to 9 ng ml\(^{-1}\)). Epitope mapping revealed that these antibodies were directed against both the receptor-binding domain (RBD) and the N-terminal domain (NTD) of the viral spike protein. Additionally, two antibodies recognized quaternary epitopes involving multiple RBDs. Cryo-electron microscopy reconstructions of these antibodies in complex with the spike protein confirmed their binding to the closed 'all RBD-down' conformation. Several of these monoclonal antibodies are promising candidates for clinical development as therapeutic and/or prophylactic agents against SARS-CoV-2.This study reports the isolation and characterization of 61 SARS-CoV-2-neutralizing monoclonal antibodies from five patients with severe COVID-19. Among these, 19 antibodies showed potent neutralization of authentic SARS-CoV-2 in vitro, with nine exhibiting very high potency (50% virus-inhibitory concentrations of 0.7 to 9 ng ml\(^{-1}\)). Epitope mapping revealed that these antibodies were directed against both the receptor-binding domain (RBD) and the N-terminal domain (NTD) of the viral spike protein. Additionally, two antibodies recognized quaternary epitopes involving multiple RBDs. Cryo-electron microscopy reconstructions of these antibodies in complex with the spike protein confirmed their binding to the closed 'all RBD-down' conformation. Several of these monoclonal antibodies are promising candidates for clinical development as therapeutic and/or prophylactic agents against SARS-CoV-2.