An auto-injector for administering a dose of a liquid medicament includes an elongate housing that contains a syringe with a hollow needle and a bung for sealing the syringe and displacing the medicament. The housing has distal and proximal ends with an orifice to be applied to an injection site. A spring mechanism, upon activation, pushes the needle from a covered position inside the housing into an advanced position through the orifice. The spring mechanism also operates the syringe to supply the dose of medicament. An activating mechanism is arranged to lock the spring mechanism in a pressurized state prior and to release the spring mechanism upon manual operation. The spring mechanism includes a torsion spring ground at one end in the housing and in a gear member on the other end. The gear member is rotatable to move another gear member to push the bung towards the proximal end.