A production system for a wind turbine component is described. The system includes an elongate mould assembly extending in a longitudinal direction, the mould assembly comprising a mould surface and having a width that varies in the longitudinal direction. First and second tracks are defined respectively on opposite longitudinal sides of the mould surface. The perpendicular distance between the respective tracks varies along the length of the track. A transport assembly is moveable relative the mould assembly in the longitudinal direction. The transport assembly includes a pair of side supports arranged to move along the respective tracks, and a gantry supported above the mould assembly by the side supports. The gantry extends transverse to the longitudinal direction. The transport assembly is configured such that the side supports move relative to one another in a direction transverse to the longitudinal direction in accordance with the varying distance between the tracks as the transport assembly moves in the longitudinal direction.