Diazomethane is a valuable C1-building block for organic synthesis but very difficult to handle and its use for scale-up is still a challenge with regard to safety. Herein we present a simple and robust continuous flow setup, that allows a safe on-demand generation of diazomethane with a productivity of 110 mmol/h. The developed two-step process starts from non-hazardous N-methylurea, generates and consumes N-methyl-N-nitrosourea (MNU) and diazomethane in-line, thus enabling a safe and convenient scale-up to multi-gram scale in a conventional synthesis laboratory.