  Fast magnetic reconnection powers explosive events throughout the universe,
from gamma-ray bursts to solar flares. Despite its importance, the onset of
astrophysical fast reconnection is the subject of intense debate and remains an
open question in plasma physics. Here we report high-cadence observations of
two reconnection-driven solar microflares obtained by the \textit{Interface
Region Imaging Spectrograph} that show persistent turbulent flows preceding
flaring. The speeds of these flows are comparable to the local sound speed
initially, suggesting the onset of fast reconnection in a highly turbulent
plasma environment. Our results are in close quantitative agreement with the
theory of turbulence-driven reconnection as well as with numerical simulations
in which fast magnetic reconnection is induced by turbulence.
