Context : Infrared dark clouds ( IRDCs ) likely represent very early stages of high-mass star/star cluster formation .

Aims : The aim is to determine the physical properties and spatial distribution of dense clumps in the IRDC MSXDC G304.74+01.32 ( G304.74 ) , and bring these characteristics into relation to theories concerning the origin of IRDCs and their fragmentation into clumps and star-forming cores .

Methods : G304.74 was mapped in the 870 \mu m dust continuum with the LABOCA bolometer on APEX .
The 870 \mu m map was compared with the 1.2 mm continuum map of the cloud by Béltran et al .
( 2006 ) .
Archival MSX and IRAS infrared data were used to study the nature and properties of the submillimetre clumps within the cloud .
The H _ { 2 } column densities were estimated using both the 870 \mu m dust emission and the MSX 8 \mu m extinction data .
The obtained values were compared with near-infrared extinction which could be estimated along a few lines of sight .
We compared the clump masses and their spatial distribution in G304.74 with those in several other recently studied IRDCs .

Results : Twelve clumps were identified from the 870 \mu m dust continuum map .
Three of them are associated with the MSX and IRAS point sources .
Moreover , one of the clumps ( SMM 6 ) is associated with two MSX 8 \mu m point-like sources .
Thus , there are 8 clumps within G304.74 which are not associated with mid-infrared ( MIR ) emission .
The H _ { 2 } column densities derived from the dust continuum and extinction data are similar .
The comparison suggests that the dust temperature may be elevated ( 20-30 K ) near the southern end of the cloud , whereas the starless clumps in the centre and in the north are cool ( T _ { d } \sim 15 K ) .
There is a high likelihood that the clump mass distributions in G304.74 and in several other IRDCs represent the samples of the same parent distribution .
In most cases the spatial distributions of clumps in IRDCs do not deviate significantly from random distributions .

Conclusions : G304.74 contains several massive clumps that are not associated with MIR emission .
On statistical grounds it is likely that some of them are or harbour high-mass starless cores ( HMSCs ) .
The fact that the clump mass distributions ( resembling the high-mass stellar IMF ) , and in some cases also the random-like spatial distributions , seem to be comparable between different IRDCs , is consistent with the idea that the origin of IRDCs , and their further sub-fragmentation down to scales of clumps is caused by supersonic turbulence in accordance with results from giant molecular clouds .