  Galaxies grow inefficiently, with only a few percent of the available gas
converted into stars each free-fall time. Feedback processes, such as
outflowing winds driven by radiation pressure, supernovae or supermassive black
hole accretion, can act to halt star formation if they heat or expel the gas
supply. We report a molecular outflow launched from a dust-rich star-forming
galaxy at redshift 5.3, one billion years after the Big Bang. The outflow
reaches velocities up to 800 km/s relative to the galaxy, is resolved into
multiple clumps, and carries mass at a rate within a factor of two of the star
formation rate. Our results show that molecular outflows can remove a large
fraction of the gas available for star formation from galaxies at high
redshift.
