Abstract Explosion gas pressure, combined with the action of an explosive stress wave, has a significant effect on the production and propagation of cracks in deep rock without a free surface. Thus, it is necessary to investigate the corresponding fracturing mechanisms and contributions of the shock wave and detonation gas towards inducing rock damage during blasting. In this work, the rock stratum is simplified as a square model with a circular borehole at its centre and modelled as a particle assembly based on the discrete element method. The shock wave is simulated as a time-varying pressure applied to the particles of the borehole. The action of the detonation gas is imitated as a quasi-static pressure on the fractures connected with the blasthole. To distinguish the role of the detonation gas in the formation and development of cracks, two primary simulation scenarios are studied: first, both the shock wave and detonation gas are simultaneously considered to simulate the blasting-induced rock damage; second, only the explosive stress wave is considered in rock blasting. Moreover, the coupling charge and decoupling charge are simulated in each scenario. In particular, based on the undirected graph theory, the authors present a new approach to efficiently determine the fracture clusters connected to the blasthole at each time-step to apply the quasi-static loads on the cracks. The results show that the shock wave plays a major role in crushing the rock near the wall of the blasthole and manufacturing a few primary radius cracks further away from the blasthole, whereas the detonation gas further extends the fractures to increase the crushed area (the additional stress caused by detonation gas is greater than the tensile strength of the rock) or separates the already formed rock fragments to increase the aperture of the cracks (the additional stress caused by the detonation gas is less than the tensile strength of the rock).