In recent years, continuous process technologies have attracted increasing attention, as a means of overcoming limitations in the repeatability and reproducibility of metal-organic framework (MOF) synthesis. Research in this area, however, has neglected to provide insight into the phenomenon leading to the formation of MOFs. In this work, we report the adaption of high-energy synchrotron powder X-ray diffraction analysis to a continuous ZIF-8 production process for online monitoring of the reaction behavior and crystallite formation during the first seconds of the MOF synthesis. It was confirmed that a diffusion-controlled growth mechanism was accelerated by additional radial diffusion processes in the flow reactor. Kinetic analysis revealed a rapid crystallite formation of ZIF-8, which was completed after 8 s of reaction time and which offers the potential for future process optimization.