We present the results of narrow-band and broad-band imaging with the Very Large Telescope of the field surrounding the radio galaxy TN J0924-2201 at $z = 5.2$. Fourteen candidate Ly α emitters with a rest-frame equivalent width of >20 Å were detected. Spectroscopy of 8 of these objects showed that 6 have redshifts similar to that of the radio galaxy. The density of emitters at the redshift of the radio galaxy is estimated to be a factor 1.5-6.2 higher than in the field, and comparable to the density of Ly α emitters in radio galaxy protoclusters at $z = 4.1, 3.1$ and 2.2. The Ly α emitters near TN J0924-2201 could therefore be part of a structure that will evolve into a massive cluster. These observations confirm that substantial clustering of Ly α emitters occurs at $z > 5$ and support the idea that radio galaxies pinpoint high density regions in the early Universe.
