  We investigate nuclear fragmentation in the central proton-nucleus and
nucleus - nucleus collisions at the energies of LHC. We argue that within the
semi-classical approximation because of fast increase with energy of cross
sections of soft and hard interactions each nucleon is stripped in the average
process off ``soft'' partons and fragments into a collection of leading quarks
and gluons with large $p_t$. Valence quarks and gluons are streaming in the
opposite directions when viewed in the c.m. of the produced system. The
resulting pattern of the fragmentation of the colliding nuclei leads to an
implosion of the quark and gluon constituents of the nuclei. The matter density
produced at the initial stage in the nucleus fragmentation region is estimated
to be $\geq$ 50 GeV/fm$^3$ at the LHC energies and probably $\geq$ 10
GeV/fm$^3$ at RHIC.
