A method and a manufacturing line for manufacturing wind turbine blades having a composite shell structure comprising a matrix material and a fibre reinforcement material by use of a resin transfer moulding process. The method comprises a manufacturing line, where wind turbine blades are formed in a number of moulds. Each number of moulds comprising at least a first mould part comprising a first mould cavity. The manufacturing line further comprises a gantry means movable along the manufacturing line. The method comprises the following steps: a) arranging fibre reinforcement material in the first mould cavity of a first mould using the gantry means, b) moving the gantry means along the manufacturing line to a second mould, c) supplying curable matrix material into the first mould cavity of the first mould, while substantially simultaneously arranging fibre reinforcement material in the first mould cavity of a second mould using the gantry means. The manufacturing line comprises a plurality of moulds for forming wind turbine blades. Each of the number of moulds comprising at least a first mould part comprising a first mould cavity.