We report on the femtosecond laser-driven antiferromagnetic (AFM) to ferromagnetic (FM) phase transition in FeRh studied with the time, element, and spatially resolved technique of magnetic X-ray resonant diffraction at the Fe L3 edge. Equiatomic FeRh undergoes a first order transition from the antiferromagnetic (AFM) to ferromagnetic (FM) phase, where the magnetization is the order parameter. The phase transition has been extensively studied theoretically and experimentally, in thermal equilibrium and in the time domain, but a precise understanding of the roles of the electronic, phononic and spin sub-systems remains elusive. Time resolved magneto-optical Kerr effect measurements suggest FM generation on sub-picosecond (ps) time scales, indicating an electronically driven phase transition. In contrast, time-resolved hard X-ray diffraction reveals nucleation and growth of FM regions on 10ps timescales, suggesting a phononic driver. Our experiments were performed at the Linac Coherent Light Source and provide microscopic insight into the very beginning of the non-equilibrium phase transition. We observe a sub-picosecond transient hinting at an ultrafast electronic seeding of the FM nucleation that spreads through the sample over the next 10ps. At later times slower domain coarsening dynamics can be seen as the system reaches thermal equilibrium.