Invasive species of intertidal algae drew little attention, even though biological invasions have been a concern around the world. The red algal bangiophyte, Phycocalidia tanegashimensis (I. Shinmura) Santiañez in Santiañez & Wynne, 2020 had been reported from the Southwest Atlantic (Brazil) and Northwest Pacific (Philippines and Japan). The appearance of P. tanegashimensis in Brazil was believed to be a recent introduction from the Indo-Pacific/North Pacific but without conclusive evidence. During a study of the biodiversity of bladed Bangiales in South China and Vietnam, we detected the presence of P. tanegashimensis in these areas using a molecular approach to the identification of the species. New distributional records of P. tanegashimensis were therefore morphologically and molecularly confirmed along the Chinese and Vietnamese coastline (part of the South China Sea) in the present study. Molecular sequence data using rbcL (ribulose bisphosphate carboxylase/oxygenase large subunit), COI-5P (cytochrome oxidase 1), and 18S rRNA genes placed P. tanegashimensis in a clade with P. acanthophora (E.C.Oliveira & Coll) Santiañez in Santiañez & Wynne, 2020, P. denticulata (Levring) Santiañez & M.J.Wynne, 2020, P. suborbiculata (Kjellman) Santiañez & M.J.Wynne, 2020 and P. vietnamensis (Tak.Tanaka & Pham) Santiañez & M.J.Wynne, 2020 as out-groups. The common morphological characters found in these species, including lobed blades and marginal denticulation, and subtropical/tropical distribution, were discussed in relation to their phylogeny. Haplotype distribution analysis indicated that P. tanegashimensis in Brazil might be an invasive species from the South China Sea. The arrival time of P. tanegashimensis from the South China Sea to Brazil was also discussed.