The present invention relates to a tower assembly system, a method of assembling a wind turbine tower and a wind turbine thereof. Three or more guidance devices may be mounted to a mounting flange in the upper end of a lower tower section and/or in the lower end of an upper tower section. The guidance device comprises a contact surface for contacting a mating contact surface on the opposite tower section. The guidance device comprises a mounting flange for mounting the device to the mounting flange of the tower section using fastening means. This allows the guidance devices to catch and guide the free hanging tower section into the correct position on the stationary tower section. This enables the assembly time to be reduced with up to 50 % compared with the present assembly methods. The guidance devices allow the workers to guide the free hanging tower section into position from the ground.