  The high extinction and extreme source crowding of the central regions of the
Milky Way are serious obstacles to the study of the structure and stellar
population of the Galactic centre (GC). Existing surveys that cover the GC
region (2MASS, UKIDSS, VVV, SIRIUS) do not have the necessary high angular
resolution. Therefore, a high-angular-resolution survey in the near infrared is
crucial to improve the state of the art. Here, we present the GALACTICNUCLEUS
catalogue, a near infrared $JHK_s$ high-angular-resolution ($0.2''$) survey of
the nuclear bulge of the Milky Way. We explain in detail the data reduction,
data analysis, calibration, and uncertainty estimation of the GALACTICNUCLEUS
survey. We assess the data quality comparing our results with previous surveys.
We obtained accurate $JHK_s$ photometry for $\sim 3.3\times10^6$ stars in the
GC detecting around 20 \% in $J$, 65 \% in $H,$ and 90 \% in $K_s$. The survey
covers a total area of $\sim0.3$ square degrees, which corresponds to $\sim
6,000$ pc$^2$. The GALACTICNUCLEUS survey reaches 5\,$\sigma$ detections for $J
\sim 22$ mag, $H \sim 21$ mag, and $K_s \sim 21$ mag. The uncertainties are
below 0.05 mag at $J \sim 21$ mag, $H \sim 19$ mag, and $K_s \sim 18$ mag. The
zero point systematic uncertainty is $\lesssim0.04$ mag in all three bands. We
present colour-magnitude diagrams for the different regions covered by the
survey.
