  We study the time evolution of wave packets of noninteracting electrons in a
two-dimensional periodic system in the presence of magnetic and electric
fields. The model includes consistently the coupling between Landau levels as
well as the periodic and external field contributions. It is shown that the
electric field produces localization along its longitudinal direction, this
effect is a physical consequence of the quantization of the energy levels with
respect to the longitudinal quasi-momentum. For incommensurate orientations of
$\mathbf{E}$ relative to the lattice the wave packet becomes localized in both
directions.
