  We present observations of the nearby (D$\sim$100\,pc) Herbig star HD~163296
taken with the vortex coronograph at Keck/NIRC2 in the L' band (3.7~$\mu$m), to
search for planetary mass companions in the ringed disc surrounding this
pre-main sequence star. The images reveal an arc-like region of scattered light
from the disc surface layers that is likely associated with the first bright
ring detected with ALMA in the $\lambda$=1.3mm dust continuum at $\sim$65~au.
We also detect a point-like source at $\sim$0\farcs5 projected separation in
the North-East direction, close to the inner edge of the second gap in the
millimetre images. Comparing the point source photometry with the atmospheric
emission models of non-accreting giant planets, we obtain a mass of 6--7~M$_J$
for a putative protoplanet, assuming a system age of 5~Myr. Based on the
contrast at a 95\% level of completeness calculated on the emission-free
regions of our images, we set upper limits for the masses of giant planets of
8--15~M$_J$, 4.5--6.5~M$_J$ and 2.5-4.0~M$_J$ at the locations of the first,
second and third gap in the millimetre dust continuum, respectively. Further
deep, high resolution thermal IR imaging of the HD~163296 system are warranted,
to confirm the presence and nature of the point source and to better understand
the structure of the dust disc.
