We have investigated low temperature growth of GaN nanostructures using halide vapor phase epitaxy on c-oriented Al2O3 and Au coated Al2O3 substrates. Depending on the III/V ratio and the growth temperature, the shape and density of the structures could be controlled. By increasing the GaCl partial pressure, the structure changed from dot-like to nanotubes. The nanotubes, which could be open or closed, were about 1 mu m long with a diameter of typically 200 nm. In addition, it was observed that the nanostructures were spontaneously nucleated at droplets of Ga or, when using Au coated Al2O3, on droplets of Au/Ga alloy. By varying the growth temperature, the inner diameter of the nanotubes could be controlled. The experimental results suggest that this approach with pre-patterned Au coated Al(2)O(3)substrates has the potential for fabrication of well-organized nanotubes with a high density.