Context : Massive condensations in giant molecular clouds ( GMCs ) are linked to the formation of high mass stars , which are the principal source of heavy elements and UV radiation , playing an important role in the evolution of galaxies . Aims : We attempt to make a complete census of massive-star formation within all of GMC G345.5+1.0 . This cloud is located one degree above the galactic plane and at 1.8 kpc from the Sun , thus there is little superposition of dust along the line-of-sight , minimizing confusion effects in identifying individual clumps . Methods : We observed the 1.2 mm continuum emission across the whole GMC using the Swedish-ESO Submillimetre Telescope ( SEST ) Imaging Bolometer Array ( SIMBA ) mounted on the SEST . Observations have a spatial resolution of 0.2 pc and cover 1 _ { { } ^ { \centerdot } } ^ { \circ } 8 \times 2 _ { { } ^ { \centerdot } } ^ { \circ } 2 in the sky with a noise of 20 mJy beam ^ { -1 } . Results : We identify 201 clumps with diameters between 0.2 and 0.6 pc , masses between 3.0 and 1.3 \times 10 ^ { 3 } M _ { \odot } , and densities between 5 \times 10 ^ { 3 } and 4 \times 10 ^ { 5 } cm ^ { -3 } . The total mass of the clumps is 1.2 \times 10 ^ { 4 } M _ { \odot } , thus the efficiency in forming these clumps , estimated as the ratio of the total clump mass to the total GMC mass , is \sim 0.02 . The clump mass distribution for masses between 10 and 10 ^ { 3 } M _ { \odot } is well-fitted by a power law dN/dM \propto M ^ { - \alpha } , with a spectral mass index \alpha of 1.7 \pm 0.1 . Given their mass distribution , clumps do not appear to be the direct progenitors of single stars . Comparing the 1.2 mm continuum emission with infrared images taken by the Midcourse Space Experiment ( MSX ) and by the SPITZER satellite , we find that at least \sim 20 % of the clumps are forming stars , and at most \sim 80 % are starless . Six massive-star forming regions ( MSFRs ) embedded in clumps and associated with IRAS point sources have mean densities of \sim 10 ^ { 5 } cm ^ { -3 } , luminosities > 10 ^ { 3 } L _ { \odot } , and spectral energy distributions that can be modeled with two dust components at different mean temperatures of 28 \pm 5 and 200 \pm 10 K . Conclusions :