This invention relates to a novel composition and method for RNA/mRNA production as well as amplification using viral RNA replicase and/or RNA-dependent RNA polymerase (RdRp) enzymes and the use of associated RNA/mRNA products thereof. The present invention can be used for manufacturing and amplifying all varieties of RNA/mRNA sequences carrying at least a replicase/RdRp-binding site in the 5′- or 3′-end, or both. The RNA/mRNA so obtained is useful for not only producing mRNA vaccines and/or RNA-based medicines but for generating the mRNA-associated proteins, peptides, and/or antibodies under an in-vitro as well as in-cell translation condition. Principally, the present invention is a novel RNA replicase/RdRp-mediated RNA/mRNA amplification method, namely Replicase Cycling Reaction (RCR). The RNA replicases involved in RCR include but not limited to viral and/or bacteriophage RNA-dependent RNA polymerases (RdRp) in either modified or non-modified mRNA and/or protein compositions, particularly coronaviral (e.g. COVID-19) and hepatitis C viral (HCV) RdRp enzymes.