[en] We theoretically study flux-flow instability in a highly disordered thin superconducting strip placed in a perpendicular magnetic field H. We find that the jump from the resistive (flux-flow) state to the normal one at quenching current I _q(H) above the critical current I _c(H) starts from the appearance of localized regions with suppressed superconductivity and fast-moving vortices near the edge of the strip, where vortices enter the superconductor and local current density is maximal. These regions propagate to the opposite edge and form highly resistive self-made Josephson-like links, which are unstable and evolve to the normal domains, which then expand along the superconducting strip. (paper)