The highest-energy gamma-rays from gamma-ray bursts (GRBs) have important implications for their radiation mechanism. Here we report the detection of gamma-rays up to 13 teraelectronvolts from the brightest GRB 221009A by the Large High Altitude Air-shower Observatory (LHAASO). The LHAASO-KM2A detector registered more than 140 gamma-rays with energies above 3 teraelectronvolts during 230 to 900 seconds after the trigger. The intrinsic energy spectrum of gamma-rays can be described by a power-law after correcting for extragalactic background light absorption. Such a hard spectrum challenges the synchrotron self-Compton scenario of relativistic electrons for the afterglow emission above several teraelectronvolts. Observations of gamma-rays up to 13 teraelectronvolts from a source with a measured redshift of z = 0.151 hints more transparency in intergalactic space than previously expected. Alternatively, one may invoke new physics such as Lorentz invariance violation or an axion origin of very high-energy signals.