  In this note, we establish certain regularity estimates for the spinor flow
introduced and initially studied in \cite{AWW2016}. Consequently, we obtain
that the norm of the second order covariant derivative of the spinor field
becoming unbounded is the only obstruction for long-time existence of the
spinor flow. This generalizes the blow up criteria obtained in \cite{Sc2018}
for surfaces to general dimensions. As another application of the estimates, we
also obtain a lower bound for the existence time in terms of the initial data.
Our estimates are based on an observation that, up to pulling back by a
one-parameter family of diffeomorphisms, the metric part of the spinor flow is
equivalent to a modified Ricci flow.
