An asymptotic solution of the magnetic induction equation in a given velocity field is constructed for large magnetic Reynolds numbers. Initially localized distributions of the magnetic field are considered. The leading term of the asymptotics is found. The expansions are proved to be rigorously valid over a finite time interval. Estimates for the residuals are given. The results are illustrated by some examples: the Hubble flow with a linear dependence of the velocity on coordinates, andABCtype flows. The solutions in these cases are expressed in terms of elementary functions.