  Particles colliding at impact parameter much larger than the effective
gravitational radius can not classically form a black hole and just scatter off
the radial potential barrier separating the particles. We show that the process
of the black hole production can still go quantum-mechanically via familiar
mechanism of the under-barrier tunneling. The mechanism is illustrated for
collision of a trans-Planckian particle and a lighter particle. Our analysis
reveals instability of trans-Planckian particles against transition to the
phase of black hole.
