Abstract: The present invention relates to a blade positioning system configured for positioning wind turbine blades at a hub of a nacelle of a wind turbine from an installation vessel at an offshore location, the blade positioning system comprising: the installation vessel comprising: — at least one lifting device configured for lifting wind turbine components, and — an auxiliary support tower extending upwardly from the installation vessel, the auxiliary support tower comprising: o a nacelle support for supporting the nacelle, o a root end moving assembly defining a guide path which extends over a vertical distance, the root end moving assembly comprising a movable root end support base and a root end support configured for supporting and guiding the root end of the blade, the root end support being connected to the movable root end support base, the root end support being movable along the guide path, the root end moving assembly being configured for moving the root end of the blade along the guide path from the eng