The high activation energy required for graphite–diamond transition limits its applicability in novel areas. To exploit fully the multifunctional properties of diamond in diverse fields, there is a necessity to explore more efficient ways for its synthesis. In this study, we have demonstrated a new approach for nanodiamonds formation by employing a commercially available low power 10 W continuous-wave fibre laser. The laser system is modulated to generate the high-pressure high temperature environment necessary for the phase conversion of graphite to diamond. The microsecond pulse duration combined with liquid confinement effect on plasma provide scope for a lower rate of supercooling, which restricts the epitaxial growth of the crystals. The sample is characterized by X-ray powder diffraction, transmission electron microscope and Raman spectroscopy, confirming the presence of different types of nanodiamonds including newly discovered n-diamond. The process offers many important advantages like scalable process, non-catalyst-based eco-friendly and cost-effective synthesis of metastable nanodiamonds. The results demonstrate the effectuality of inexpensive commercial lasers towards attaining the localized extreme environment necessary for direct phase conversion of diamond materials.