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The GLIMPSE archive was used to obtain 3.6--8.0micron, point sourcephotometry and images for 381 massive protostellar candidates lying in theGalactic mid-plane. The colours, magnitudes and spectral indicies of sources ineach of the 381 target fields were analysed and compared with the predictionsof 2D radiative transfer model simulations. Although no discernable embeddedclusters were found in any targets, multiple sources or associations ofredenned young stellar objects were found in many sources indicatingmultiplicity at birth. The spectral index ($\alpha$) of these point sources in3.6--8.0mum bands display large values of $\alpha$=2--5. A color-magnitudeanalog plot was used to identify 79 infrared counterparts to the HMPOs. Compactnebulae are found in 75% of the detected sources with morphologies that can bewell described by core-halo, cometary, shell-like and bipolar geometriessimilar to those observed in ultra-compact HII regions. The IRAC band SEDs ofthe IR counterparts of HMPOs are best described to represent YSOs with a massrange of 8--20\msun in their Class I stages when compared with 2D radiativetransfer models. They also suggest that the high $\alpha$ values representreprocessed star/star+disk emission that is arising in the dense envelopes.Thus we are witnessing the luminous envelopes around the protostars rather thantheir photospheres or disks. We argue that the compact infrared nebulae likelyreflect the underlying physical structure of the dense cores and are found toimitate the morphologies of known UCHII regions. Our results favour models ofcontinuuing accretion involving both molecular and ionised accretion componentsto build the most massive stars rather than purely molecular rapid accretionflows.

Spitzer-IRAC GLIMPSE of high mass protostellar objects. I Infrared point sources and nebulae