On the recent post about the Sam Ka Tsuen pier, Stephen Davies noted that it was almost definitely built by local workers, supervised by the Royal Engineers. I've moved the other comments about that topic here, as it is a bigger subject that deserves its own page.
If you can add any more information, please let us know in the comments below.
David - the only HK-related source that springs to mind is the article in Papers on subjects connected with the duties of the Royal Engineers, vol X, 1849, pp.153-155 by Major Edward Aldrich RE (yes, that's the one, the CO of the RE in HK, who also worked for PWD) entitled "Description of the Mat Covering Sheds used at Hong-Kong in the erection of the Ordnance Buildings, and of the mode adopted by the Chinese in transporting and raising heavy Weights for these Buildings", which has a couple of charming drawings by Bernard Collinson illustrating the points. This makes it clear, at least in the erection of barracks (and I can see no reason why it would not apply to the erection of anything other than structures of what's known as field, or combat engineering), local labour and contractors were used.
Elizabeth Vincent, Substance and practice building technology and the Royal Engineers in Canada, Environment Canada, Studies in Archaeology Architecture and History: National Historic Sites Parks Service Environment Canada, 1993, p.7 notes, writing of the earliest work in Canada in the first two or three decades of the 19th century, "Construction of military buildings was carried out under the supervision of officers of the Corps of Royal Engineers, but the actual work was increasingly done by local builders under contract to the Ordnance Department." In her longer discussion of actual procedures (pp.13-29), she notes that, "By the mid-1830s the expectation appeared to be that most of the work included in the annual Ordnance and Barrack estimates would be performed by local contractors. For new works precise specifications and plans were usually drawn up before the work was authorized." But she does go on to reveal that the procedures (natch!) were typically bureaucratic and convoluted, "It was not the engineer officers who were directly responsible for obtaining contracts for construction work and building materials. The Commissariat had the responsibility for preparing tenders and contracting for building materials and construction work. The specifications for materials or workmanship were prepared by the engineer officers for the information of the Commissariat. who would then advertise for tenders." Obviously continuing reforms to the military at the end of the 19th century (Cardwell and then Childers) probably streamlined things a bit, but it seems clear that the system of RE design and supervision and locally contracted materials and construction had become the norm.
Vincent is a very good source on how the RE actually worked on local fortification and other military work in the British empire system, though she focusses more on the early years, rather than the end of the 19th century when Canada had become a significant economy in its own right. In sum, by the end of the 19th century I think it reasonable to conclude that almost all military commissioned construction work in British colonies, etc., whilst designed by the RE, would have been constructed by local contractors.
The supply of materials was an Empire preference system, with requirements to source from British manufacturers unless it was clear on either military or feasibility grounds that local sources were best. I would suggest that very large granite blocks were probably not sourced from Britain or, indeed, probably anywhere other than locally, since as Sam Poon and his collaborators have shown, HK's granite business had been booming well before the British arrived, and boomed further with the growth of government and military contracts.
Contractors in Hong Kong
I found two more examples of contractors being used on military sites in Hong Kong in the 19th century. The first is from Thomas Lyster, writing in 1865. His letters were collected and published in With Gordon in China: Letters from Thomas Lyster, Lieutenant Royal Engineers, which is available to read online. At the time he wrote the letters I quote from below, he was living and working in Kowloon.
p.263, 9 May 1865: 'The greater number of the natives about here are what they call Hakka men, that is the Chinese of "gipsy". I have been at war with them since I came here, as they are employed as stone-cutters, and they bring bad stone to work, which they won't take away; so I get it broken up, and they attack my men. I sent some of them to prison.'
p.269, 27 June 1865: 'I have had a deal of fighting with the contractors here. They are awful rogues. . . .'
The other is from The Forts Protection Ordinance, 1891. The first part of point 1 lists the military men who are allowed to enter 'such battery, field-work or fortification', and says anyone else will be fined or imprisoned. But a second paragraph grants an exception to contractors and their staff:
'Any order granted to any contractor employed by the officer commanding the Royal Engineers shall cover all Chinese labourers specifically mentioned in such order actually employed on work in any battery, field-work or fortification.'