The formation of hot tears during the start-up phase of DC-cast extrusion billets is studied experimentally and numerically. Hot tears may form in the centre on top of the starting block and extend throughout the whole ingot. Particular attention was paid to the casting speed which is one of the process parameters that strongly affects the hot tearing tendency. Different ramping of the casting speed during the start-up phase (casting recipes) were studied and results were compared with five casting trials carried out at Hydro Aluminium with the AA6060 alloy. For all trials, a cone shaped steel starting block has been used and temperature measurements were carried out in both the ingot and the starting block. Three trials resulted in the formation of hot tears of different lengths, while the remaining two castings were carried out without any starting cracks. The temperature measurements where used to calculate the coupled evolution of the temperature, velocity and stress fields during the castings using the ALSIM/ALSPEN model, in which the computation of the liquid pressure drop within the mush (transient Rappaz-Drezet-Gremaud, RDG, hot tearing criterion) was implemented. The comparison between the model results and the measured starting crack lengths shows a clear correlation between the calculated strain rates and the RDG predictions.