Amplification of magnetic flux and electric polarization fields caused by a plasma streaming at relativistic velocity in to a magnetic field is discussed. It is shown that the electrostatic polarization field that arises in a plasma beam streaming across magnetic field lines at relativistic velocities will cause an amplification of the magnetic flux. This effect is in complete contrast to the expulsion of the magnetic field from the plasma interior that can be expected in high βK plasmas. The amplification is shown to be caused by the relativistic motion of the space charge layers setting up the polarization field. Three dimensional electromagnetic particle-in-cell simulations that support this theory are presented.