  The first stars are predicted to have formed within 200 million years after
the Big Bang, initiating the cosmic dawn. A true first star has not yet been
discovered, although stars with tiny amounts of elements heavier than helium
('metals') have been found in the outer regions ('halo') of the Milky Way. The
first stars and their immediate successors should, however, preferentially be
found today in the central regions ('bulges') of galaxies, because they formed
in the largest over-densities that grew gravitationally with time. The Milky
Way bulge underwent a rapid chemical enrichment during the first 1-2 billion
years, leading to a dearth of early, metal-poor stars. Here we report
observations of extremely metal-poor stars in the Milky Way bulge, including
one star with an iron abundance about 10,000 times lower than the solar value
without noticeable carbon enhancement. We confirm that the most metal-poor
bulge stars are on tight orbits around the Galactic Centre, rather than being
halo stars passing through the bulge, as expected for stars formed at redshifts
greater than 15. Their chemical compositions are in general similar to typical
halo stars of the same metallicity although intriguing differences exist,
including lower abundances of carbon.
