and

Aims. AX J1845.0-0433 is a transient high-mass X-ray binary discovered by ASCA. The source displays bright and short flares observed by INTEGRAL. The transient behaviour and bright and short flares are studied to understand both the accretion mechanisms and nature of the source. Methods. Public INTEGRAL data and a pointed XMM-Newton observation are used to study in detail the flaring and quiescent phases. Results. AX J1845.0-0433 is a persistent X-ray binary with a O9.5I supergiant companion, emitting at a low 0.2-100 keV luminosity of ~$10^{35}\ {\rm erg}\,{\rm s}^{-1}$ with seldom flares and reaching luminosities of $10^{36}\ {\rm erg}\,{\rm s}^{-1}$. The most accurately measured X-ray position is RA (2000)=18h45m01.4s and Dec =-04$^\circ{33}^\prime{57.7}\arcsec$ (2″). Variability factors of 50 are observed on timescales as short as hundreds of seconds. The broad-band spectrum is typical of wind-fed accreting pulsars with an intrinsic absorption of $N_{\mathrm{H}}=(2.6\pm0.2)\times 10^{22}\ \mathrm{cm}^{-2}$, a hard continuum of $\Gamma=(0.7{-}0.9)\pm0.1$, and a high-energy cutoff at $E_{\mathrm{cut}}=16_{-3}^{+5}$ keV. An excess at low energies is also observed fitted with a black body with a temperature of $kT=0.18\pm0.05$ keV. Optically-thin and highly-ionised iron (Fe XVIII-XIX) located close to the supergiant star is detected during the quiescence phase. The spectral shape of the X-ray continuum remains unchanged. In contrast to the persistent quiescent emission, the flare characteristics suggest that clumps of mass $M\sim 10^{22}$ g are formed within the stellar wind of the supergiant companion