We analyse Prognoz-8 observations of plasma and magnetic field at the dawn flank (Y gsm=−9.0 to −6.5 R E) of the near-Earth tail (R=11.5−7.3 R E) during the first ∼3 hours of a strong substorm with multiple intensifications. In this region of the magnetosphere the cold boundary populations (Low Latitude Boundary Layer and plasma mantle) advance against the retreating Central Plasma Sheet during the gradual growth phase and during the stretching episodes preceding substorm intensifications. Our observations are significant for a self-consistent model of plasma and magnetic field dynamics during substorms.