Multijet events at large transverse momentum (pTpT) are measured at s=13 TeVs =13TeV using data recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 36.3 fb−136.3fb−1. The multiplicity of jets with pT>50 GeVpT>50GeV that are produced in association with a high-pTpT dijet system is measured in various ranges of the pTpT of the jet with the highest transverse momentum and as a function of the azimuthal angle difference Δϕ1,2Δϕ1,2 between the two highest pTpT jets in the dijet system. The differential production cross sections are measured as a function of the transverse momenta of the four highest pTpT jets. The measurements are compared with leading and next-to-leading order matrix element calculations supplemented with simulations of parton shower, hadronization, and multiparton interactions. In addition, the measurements are compared with next-to-leading order matrix element calculations combined with transverse-momentum dependent parton densities and transverse-momentum dependent parton shower.