Context : Active galactic nuclei ( AGNs ) have typically been discovered in massive galaxies of high metallicity .

Aims : We attempt to increase the number of AGN candidates in low metallicity galaxies .
We present VLT/UVES and archival VLT/FORS1 spectroscopic and NTT/SUSI2 photometric observations of the low-metallicity emission-line galaxy Tol 2240–384 and perform a detailed study of its morphology , chemical composition , and emission-line profiles .

Methods : The profiles of emission lines in the UVES and FORS1 spectra are decomposed into several components with different kinematical properties by performing multicomponent fitting with Gaussians .
We determine abundances of nitrogen , oxygen , neon , sulfur , chlorine , argon , and iron by analyzing the fluxes of narrow components of the emission lines using empirical methods .
We verify with a photoionisation model that the physics of the narrow-line component gas is similar to that in common metal-poor galaxies .

Results : Image deconvolution reveals two high-surface brightness regions in Tol 2240–384 separated by 2.4 kpc .
The brightest southwestern region is surrounded by intense ionised gas emission that strongly affects the observed B - R colour on a spatial scale of \sim 5 kpc .
The profiles of the strong emission lines in the UVES spectrum are asymmetric and all these lines apart from H \alpha and H \beta can be fitted by two Gaussians of FWHM \sim 75 – 92 km s ^ { -1 } separated by \sim 80 km s ^ { -1 } implying that there are two regions of ionised gas emitting narrow lines .
The oxygen abundances in both regions are equal within the errors and in the range 12+log O/H = 7.83 – 7.89 .
The shapes of the H \alpha and H \beta lines are more complex .
In particular , the H \alpha emission line consists of two broad components of FWHM \sim 700 km s ^ { -1 } and 2300 km s ^ { -1 } , in addition to narrow components of two regions revealed from profiles of other lines .
This broad emission in H \alpha and H \beta associated with the high-excitation , brighter southwestern H ii region of the galaxy is also present in the archival low- and medium-resolution VLT/FORS1 spectra .
The extraordinarily high luminosity of the broad H \alpha line of 3 \times 10 ^ { 41 } erg s ^ { -1 } can not be accounted for by massive stars at different stages of their evolution .
The broad H \alpha emission persists over a period of 7 years , which excludes supernovae as a powering mechanism of this emission .
This emission most likely arises from an accretion disc around a black hole of mass \sim 10 ^ { 7 } M _ { \odot } .

Conclusions :