The most common resistance mechanism to carbapenems is the production of carbapenemases. In 2021, the Pan American Health Organization warned of the emergence and increase in new carbapenemase combinations inEnterobacteralesin Latin America. In this study, we characterized fourKlebsiella pneumoniaeisolates harboringblaKPCandblaNDMfrom an outbreak during the COVID-19 pandemic in a Brazilian hospital. We assessed their plasmids’ transference ability, fitness effects, and relative copy number in different hosts. TheK. pneumoniaeBHKPC93 and BHKPC104 strains were selected for whole genome sequencing (WGS) based on their pulsed-field gel electrophoresis profile. The WGS revealed that both isolates belong to ST11, and 20 resistance genes were identified in each isolate, includingblaKPC-2andblaNDM-1. TheblaKPCgene was present on a ~56 Kbp IncN plasmid and theblaNDM-1gene on a ~102 Kbp IncC plasmid, along with five other resistance genes. Although theblaNDMplasmid contained genes for conjugational transfer, only theblaKPCplasmid conjugated toE. coliJ53, without apparent fitness effects. The minimum inhibitory concentrations (MICs) of meropenem/imipenem against BHKPC93 and BHKPC104 were 128/64 and 256/128 mg/L, respectively. Although the meropenem and imipenem MICs againstE. coliJ53 transconjugants carrying theblaKPCgene were 2 mg/L, this was a substantial increment in the MIC relative to the original J53 strain. TheblaKPCplasmid copy number was higher inK. pneumoniaeBHKPC93 and BHKPC104 than inE. coliand higher than that of theblaNDMplasmids. In conclusion, two ST11K. pneumoniaeisolates that were part of a hospital outbreak co-harboredblaKPC-2andblaNDM-1. TheblaKPC-harboring IncN plasmid has been circulating in this hospital since at least 2015, and its high copy number might have contributed to the conjugative transfer of this particular plasmid to anE. colihost. The observation that theblaKPC-containing plasmid had a lower copy number in thisE. colistrain may explain why this plasmid did not confer phenotypic resistance against meropenem and imipenem.