Context : Recent near-infrared data have contributed to the discovery of new ( obscured ) massive stellar clusters and massive stellar populations in previously known clusters in our Galaxy .
These discoveries lead us to view the Milky Way as an active star-forming machine .

Aims : The main purpose of this work is to determine physically the main parameters ( distance , size , total mass and age ) of Masgomas-1 , the first massive cluster discovered by our systematic search programme .

Methods : Using near-infrared ( J , H , and K _ { S } ) photometry we selected 23 OB-type and five red supergiant candidates for multi-object H - and K -spectroscopy and spectral classification .

Results : Of the 28 spectroscopically observed stars , 17 were classified as OB-type , four as supergiants , one as an A-type dwarf star , and six as late-type giant stars .
The presence of a supergiant population implies a massive nature of Masgomas-1 , supported by our estimate of the cluster initial total mass of ( 1.94 \pm 0.28 ) \cdot 10 ^ { 4 } { M } _ { \odot } , obtained after integrating the cluster mass function .
The distance estimate of 3.53 ^ { +1.55 } _ { -1.40 } kpc locates the cluster closer than the Scutum–Centaurus base but still within that Galactic arm .
The presence of an O9 V star and red supergiants in the same population indicates that the cluster age is in the range of 8 to 10 Myr .

Conclusions :