Because of the intense brightness of the OB-type multiple star system \sigma Ori , the low-mass stellar and substellar populations close to the centre of the very young \sigma Orionis cluster is poorly know .
I present an IJHK _ { s } survey in the cluster centre , able to detect from the massive early-type stars down to cluster members below the deuterium burning mass limit .
The near-infrared and optical data have been complemented with X-ray imaging .
Ten objects have been found for the first time to display high-energy emission .
Previously known stars with clear spectroscopic youth indicators and/or X-ray emission define a clear sequence in the I vs . I - K _ { s } diagram .
I have found six new candidate cluster members that follow this sequence .
One of them , in the magnitude interval of the brown dwarfs in the cluster , displays X-ray emission and a very red J - K _ { s } colour , indicative of a disc .
Other three low-mass stars have excesses in the K _ { s } band as well .
The frequency of X-ray emitters in the area is 80 \pm 20 % .
The spatial density of stars is very high , of up to 1.6 \pm 0.1 arcmin ^ { -2 } .
There is no indication of lower abundance of substellar objects in the cluster centre .
Finally , I also report two cluster stars with X-ray emission located at only 8000–11000 AU to \sigma Ori AB , two sources with peculiar colours and an object with X-ray emission and near-infrared magnitudes similar to those of previously-known substellar objects in the cluster .