  Several fast radio bursts have been discovered recently, showing a bright,
highly dispersed millisecond radio pulse. The pulses do not repeat and are not
associated with a known pulsar or gamma-ray burst. The high dispersion suggests
sources at cosmological distances, hence implying an extremely high radio
luminosity, far larger than the power of single pulses from a pulsar. We
suggest that a fast radio burst represents the final signal of a supramassive
rotating neutron star that collapses to a black hole due to magnetic braking.
The neutron star is initially above the critical mass for non-rotating models
and is supported by rapid rotation. As magnetic braking constantly reduces the
spin, the neutron star will suddenly collapse to a black hole several thousand
to million years after its birth. We discuss several formation scenarios for
supramassive neutron stars and estimate the possible observational signatures
{making use of the results of recent numerical general-relativistic
calculations. While the collapse will hide the stellar surface behind an event
horizon, the magnetic-field lines will snap violently. This can turn an almost
ordinary pulsar into a bright radio "blitzar": Accelerated electrons from the
travelling magnetic shock dissipate a significant fraction of the magnetosphere
and produce a massive radio burst that is observable out to z>0.7. Only a few
percent of the neutron stars needs to be supramassive in order to explain the
observed rate. We suggest that fast radio bursts might trace the solitary
formation of stellar mass black holes at high redshifts. These bursts could be
an electromagnetic complement to gravitational-wave emission and reveal a new
formation and evolutionary channel for black holes that are not seen as
gamma-ray bursts. Radio observations of these bursts could trace the
core-collapse supernova rate throughout the universe.
