  We calculate cross sections for $g g \to Q \bar Q Q \bar Q$ in the
high-energy approximation in the mixed (longitudinal momentum fraction, impact
parameter) and momentum space representations. Besides the total cross section
as a function of subsystem energy also differential distributions (in quark
rapidity, transverse momentum, $Q Q$, $Q \bar Q$ invariant mass) are presented.
The elementary cross section is used to calculate production of $(c \bar c) (c
\bar c)$ in single-parton scattering (SPS) in proton-proton collisions. We
present integrated cross section as a function of proton-proton center of mass
energy as well as differential distribution in $M_{(c \bar c)(c \bar c)}$. The
results are compared with corresponding results for double-parton scattering
(DPS) discussed recently in the literature. We find that the considered SPS
contribution to $(c \bar c)(c \bar c)$ production is at high energy ($\sqrt{s}
>$ 5 TeV) much smaller than that for DPS contribution.
