We establish a local-in-space short-time smoothing effect for the Navier-Stokes equations in the half space. The whole space analogue, due to Jia and Šverák [21], is a central tool in two of the authors' recent work on quantitative Lx3 blow-up criteria [7]. The main difficulty is that the non-local effects of the pressure in the half space are much stronger than in the whole space. As an application, we demonstrate that the critical Lx3 norm must concentrate at scales ∼T⁎−t in the presence of a Type I blow-up.