Embodiments of the invention relate to a method and apparatus for continuously casting a metal slab. The method involves continuously introducing molten metal into an inlet of a casting cavity defined between advancing casting surfaces, cooling the metal in the cavity to form a metal slab, and discharging the slab from the cavity through an outlet. The casting surfaces have an ability to remove heat from the metal but this ability is reduced, thus reducing heat flux, for at least one of the casting surfaces in a region of the cavity spaced from both the inlet and the outlet and extending transversely to the casting direction. This reduced ability to remove heat is relative to such ability of the casting surface in immediately adjacent upstream and downstream regions of the cavity. The apparatus may be a twin belt caster or other form of continuous caster modified to perform the method.