An extensive investigation of the temperature dependence of Raman spectra has been carried out on WO3 powders from room temperature to 800 degrees C. In particular the orthorhombic-to-tetragonal phase transition occurring at about 740 degrees C has been studied for the first time. The Raman active mode at 710 cm(-1) of the orthorhombic phase disappears from the spectrum at temperature below the phase transition point and the Raman activity in the tetragonal phase results very low. A comparative study of hydrogenated tungsten bronzes HxWO3 (x less than or equal to 0.23), where the same transition sequence is driven by an increase of the proton concentration from x = 0 to 0.23, reveals similar behaviour of the high frequency Raman active modes, which are better resolved due to the weaker anharmonic interactions.