  Comprehensive results on the production of unidentified charged particles,
$\pi^{\pm}$, $\rm{K}^{\pm}$, $\rm{K}^{0}_{S}$, $\rm{K}$*(892)$^{0}$, $\rm{p}$,
$\overline{\rm{p}}$, $\phi$(1020), $\Lambda$, $\overline{\Lambda}$, $\Xi^{-}$,
$\overline{\Xi}^{+}$, $\Omega^{-}$ and $\overline{\Omega}^{+}$ hadrons in
proton-proton (pp) collisions at $\sqrt{s}$ = 7 TeV at midrapidity ($|y| <
0.5$) as a function of charged-particle multiplicity density are presented. In
order to avoid auto-correlation biases, the actual transverse momentum
($p_{\rm{T}}$) spectra of the particles under study and the event activity are
measured in different rapidity windows. In the highest multiplicity class, the
charged-particle density reaches about 3.5 times the value measured in
inelastic collisions. While the yield of protons normalized to pions remains
approximately constant as a function of multiplicity, the corresponding ratios
of strange hadrons to pions show a significant enhancement that increases with
increasing strangeness content. Furthermore, all identified particle to pion
ratios are shown to depend solely on charged-particle multiplicity density,
regardless of system type and collision energy. The evolution of the spectral
shapes with multiplicity and hadron mass shows patterns that are similar to
those observed in p-Pb and Pb-Pb collisions at LHC energies. The obtained
$p_{\rm{T}}$ distributions and yields are compared to expectations from
QCD-based pp event generators as well as to predictions from thermal and
hydrodynamic models. These comparisons indicate that traces of a collective,
equilibrated system are already present in high-multiplicity pp collisions.
