This article reports on a search for dijet resonances using 132 fb-1 of pp collision data recorded at s=13 TeV by the ATLAS detector at the Large Hadron Collider. The search is performed solely on jets reconstructed within the ATLAS trigger to overcome bandwidth limitations imposed on conventional single-jet triggers, which would otherwise reject data from decays of sub-TeV dijet resonances. Collision events with two jets satisfying transverse momentum thresholds of pT≥85 GeV and jet rapidity separation of |y*|<0.6 are analysed for dijet resonances with invariant masses from 375 to 1800 GeV. A data-driven background estimate is used to model the dijet mass distribution from multijet processes. No significant excess above the expected background is observed. Upper limits are set at 95% confidence level on coupling values for a benchmark leptophobic axial-vector Z′ model and on the production cross section for a new resonance contributing a Gaussian-distributed line-shape to the dijet mass distribution.