A very young component in the pre-eminent starburst region of the Small Magellanic Cloud

Context. Despite extensive research on various components of the N66/NGC 346 complex, few studies have so far focused on N66A, which is a special object in the whole complex and therefore deserves scrutiny. The study of this compact HII region and its fellow objects seems important in the framework of massive star formation in the Magellanic Clouds. Aims. We present a study of the compact HII region N66A in the SMC pre-eminent starburst region N66/NGC 346. Methods. This analysis is based mainly on our optical ESO NTT observations, both imaging and spectroscopy, coupled with archive HST ACS data and Spitzer infrared images (IRAC 3.6, 4.5, 5.8, and 8.0 mu m). Results. We derive a number of physical characteristics of the compact HII region N66A. For the first time using spectroscopy, we present the spectral classification of the main exciting star of N66A. Its spectral features indicate that it is a main-sequence massive star of type O8. We compare this result with that based on the stellar Lyman continuum flux estimated from the ionized gas H beta flux. The compact HII region belongs to a rare class of HII regions in the Magellanic Clouds, called high-excitation blobs (HEBs). We propose that N66A probably represents a very young massive star formation event in the N66 complex that has a range of ages.