  We investigate Extremely Red Quasars (ERQs), a remarkable population of
heavily-reddened quasars at redshift z$\sim$2 - 3 that might be caught during a
short-lived 'blow-out' phase of quasar/galaxy evolution. We perform a near-IR
observational campaign using Keck/NIRSPEC, VLT/X-shooter and Gemini/GNIRS to
measure rest-frame optical spectra of 28 ERQs with median infrared luminosity
$\langle$log L(erg/s)$\rangle$ $\sim$46.2. They exhibit the broadest and most
blue-shifted [OIII] $\lambda$4959,5007 emission lines ever reported, with
widths (w90) ranging between 2053 and 7227 km/s, and maximum outflow speeds
(v98) up to 6702 km/s. ERQs on average have [OIII] outflows velocities about 3
times larger than those of luminosity-matched blue quasar samples. We show that
the faster [OIII] outflows in ERQs are strongly correlated with their extreme
red colors and not with radio-loudness, larger quasar luminosities, nor higher
Eddington ratios. We estimate for these objects that at least 3-5 per cent of
their bolometric luminosity is being converted into the kinetic power of the
observed wind. Our results reveal that ERQs have the potential to strongly
affect the evolution of host galaxies.
