The KM3NeT collaboration is currently building the next-generation large-volume (km$^3$-size) water-Cherenkov neutrino telescopes at the bottom of the Mediterranean sea. The denser of the two detectors under construction is called KM3NeT/ORCA, which is optimised for the detection of atmospheric neutrinos with energies above ${\sim}1$~GeV. The main research target of the KM3NeT/ORCA detector is the measurement of the neutrino mass ordering and atmospheric neutrino oscillation parameters. The projected sensitivity of the detector to the neutrino mass ordering is shown, alongside prospects for early analyses of data collected with a small sub-array of the detector during construction phase.