Amplification of magnetic flux and electric polarization fields caused by a plasma streaming at relativistic velocity into a magnetic held is discussed. It is shown that the electrostatic polarization held that arises in a plasma beam streaming across magnetic held lines at relativistic velocities will cause 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, where βK is the kinetic energy density in the plasma stream divided by the energy density in the magnetic field. The amplification is shown to be caused by the relativistic motion of the space charge layers setting up the polarization field. 3-D electromagnetic particle-in-cell simulations that support this theory are presented.