  We present results from a radio survey for variable and transient sources on
15-min timescales, using the Australian SKA Pathfinder (ASKAP) pilot surveys.
The pilot surveys consist of 505 h of observations conducted at around 1 GHz
observing frequency, with a total sky coverage of 1476 deg$^2$. Each
observation was tracked for approximately 8-10h, with a typical rms sensitivity
of $\sim$30 $\mu$jy/beam and an angular resolution of $\sim$12 arcsec. The
variability search was conducted within each 8-10h observation on a 15-min
timescale. We detected 38 variable and transient sources. Seven of them are
known pulsars, including an eclipsing millisecond pulsar, PSR J2039$-$5617.
Another eight sources are stars, only one of which has been previously
identified as a radio star. For the remaining 23 objects, 22 are associated
with active galactic nuclei or galaxies (including the five intra-hour
variables that have been reported previously), and their variations are caused
by discrete, local plasma screens. The remaining source has no multi-wavelength
counterparts and is therefore yet to be identified. This is the first
large-scale radio survey for variables and transient sources on minute
timescales at a sub-mJy sensitivity level. We expect to discover $\sim$1 highly
variable source per day using the same technique on the full ASKAP surveys.
