  The average transverse momentum $\langle p_{\rm T}\rangle$ versus the
charged-particle multiplicity $N_{\rm ch}$ was measured in p-Pb collisions at a
collision energy per nucleon-nucleon pair $\sqrt{s_{\rm NN}}=5.02$ TeV and in
pp collisions at collision energies of $\sqrt{s}=0.9$, 2.76, and 7 TeV in the
kinematic range $0.15<p_{\rm T}<10.0$ GeV/$c$ and $|\eta|<0.3$ with the ALICE
apparatus at the LHC. These data are compared to results in Pb-Pb collisions at
$\sqrt{s_{\rm NN}}=2.76$ TeV at similar charged-particle multiplicities. In pp
and p-Pb collisions, a strong increase of $\langle p_{\rm T}\rangle$ with
$N_{\rm ch}$ is observed, which is much stronger than that measured in Pb-Pb
collisions. For pp collisions, this could be attributed, within a model of
hadronizing strings, to multiple-parton interactions and to a final-state color
reconnection mechanism. The data in p-Pb and Pb-Pb collisions cannot be
described by an incoherent superposition of nucleon-nucleon collisions and pose
a challenge to most of the event generators.
