  We present a new approach for the prompt production of quarkonia which is
based on the $k_T$-factorization method. The production of even C-parity
quarkonia proceeds via the fusion of two (off-shell) gluons. Especially in the
kinematics of the LHCb experiment these processes are thus expected to be a
sensitive probe of the small-$x$ gluon distribution. We calculate the relevant
off-shell matrix elements in terms of the light-front wave functions of the
quarkonium states. We present our results for scalar and pseudoscalar charmonia
and discuss photon transition form factors as well as cross sections for prompt
hadroproduction.
  We compare our results for the $\eta_c$ to recent LHCb data.
