  We present new three-dimensional (3D) interstellar dust reddening maps of the
Galactic plane in three colours, E(G-Ks), E(Bp-Rp) and E(H-Ks). The maps have a
spatial angular resolution of 6 arcmin and covers over 7000 deg$^2$ of the
Galactic plane for Galactic longitude 0 deg $<$ $l$ $<$ 360 deg and latitude
$|b|$ $<$ $10$ deg. The maps are constructed from robust parallax estimates
from the Gaia Data Release 2 (Gaia DR2) combined with the high-quality optical
photometry from the Gaia DR2 and the infrared photometry from the 2MASS and
WISE surveys. We estimate the colour excesses, E(G-Ks), E(Bp-Rp) and E(H-Ks),
of over 56 million stars with the machine learning algorithm Random Forest
regression, using a training data set constructed from the large-scale
spectroscopic surveys LAMOST, SEGUE and APOGEE. The results reveal the
large-scale dust distribution in the Galactic disk, showing a number of
features consistent with the earlier studies. The Galactic dust disk is clearly
warped and show complex structures possibly spatially associated with the
Sagittarius, Local and Perseus arms. We also provide the empirical extinction
coefficients for the Gaia photometry that can be used to convert the colour
excesses presented here to the line-of-sight extinction values in the Gaia
photometric bands.
