  We present the goals, strategy and first results of the OmegaWhite survey: a
wide-field high-cadence $g$-band synoptic survey which aims to unveil the
Galactic population of short-period variable stars (with periods $<$ 80 min),
including ultracompact binary star systems and stellar pulsators. The ultimate
goal of OmegaWhite is to cover 400 square degrees along the Galactic Plane
reaching a depth of $g = $ 21.5 mag (10$\sigma$), using OmegaCam on the VLT
Survey Telescope (VST). The fields are selected to overlap with surveys such as
the Galactic Bulge Survey (GBS) and the VST Photometric H$\alpha$ Survey of the
Southern Galactic Plane (VPHAS+) for multi-band colour information. Each field
is observed using 38 exposures of 39 s each, with a median cadence of $\sim$2.7
min for a total duration of two hours. Within an initial 26 square degrees, we
have extracted the light curves of 1.6 million stars, and have identified 613
variable candidates which satisfy our selection criteria. Furthermore, we
present the light curves and statistical properties of 20 sources which have
the highest-likelihood of being variable stars. One of these candidates
exhibits the colours and light curve properties typically associated with
ultracompact AM CVn binaries, although its spectrum exhibits weak Balmer
absorption lines and is thus not likely to be such a binary system. We also
present follow-up spectroscopy of five other variable candidates, which
identifies them as likely low-amplitude $\delta$ Sct pulsating stars.
