Rapid optical flaring of an unprecedented type was detected from a transient Galactic high‐energy source, SWIFT J195509.6+261406 [1]. On June 10, 2007, Swift‐BAT triggered on GRB 070610, which turned out to be a previously unknown X‐ray transient in the Galaxy. Optical emission following this transient was observed after only 421 s with the high‐time‐resolution single‐photon counting photometer OPTIMA. Measurements continued for the following 5 nights.We detected very strong optical flares (>6 mag) with extremely short timescales: duration of individual flares 2–100 s, shortest variability timescales 0.4 s. The scale and magnitude of the observed variability combined with a distance estimate of 4–8 kpc indicate a non‐thermal origin of the observed radiation. The morphology of the optical flares is reminiscent of X‐ray outbursts of SGRs. The time resolution and high signal‐to‐noise ratio during the brightest optical outbursts allow to compute their Fourier power spectral density. Features similar to QPOs a...