  We report results of a numerical study of non-interacting electrons moving in
a random potential in two dimensions in the presence of a weak perpendicular
magnetic field. We study the topological properties of the electronic
eigenstates within a tight binding model. We find that in the weak magnetic
field or strong randomness limit, extended states float up in energy. Further,
the localization length is found to diverge at the insulator phase boundary
with the same exponent $\nu$ as that of the isolated lowest Landau band (high
magnetic field limit).
