We present time-resolved synchrotron x-ray diffraction measurements to study kinetics associated with theliquid-solid and solid-solid high-pressure phase transitions in Kr under dynamic loading in a dynamic-diamondanvil cell. The results show a strong compression-rate dependence of the solidification/melting process in liquidKr. The analysis of the compression-rate dependent melting/solidification, using an Avrami equation with theparameter n = 1, indicates a spontaneous nucleation and one-dimensional growth mechanism. In contrast, theface-centered-cubic to metastable hexagonal close-packed transition in solid Kr occurs rapidly at 0.8 GPa nearthemelting line, which has negligible compression-rate dependence within the range of compression rates studied(0.004–13 GPa/s).