The origin of cosmic rays (CRs) is a fundamental problem in astrophysics. Supernova remnants (SNRs) are regarded as the most promising source candidates for the CRs in our Galaxy. However, the recent multi-wavelength observations reveal that SNRs cannot account for all the Galactic CRs, especially for the ultra high energy band (~ 1PeV). Due to the particle acceleration capacity, young massive clusters (YMCs) are considered as an alternative CR source population. The recent gamma-ray observations found a universal hard gamma-ray spectra and 1/r CR distributions in the vicinity of such sources. The efficiency of conversion of kinetic energy of stellar winds to CRs can be as high as 10 percent implying that the YMCs may operate as CR accelerators with a dominant contribution to the flux of highest energy galactic CRs.
