Gammon Construction has been awarded a £300m contract by the Hong Kong government to construct a sewage conveyance system.
The contract is the largest single civil engineering contract ever won by Gammon.
The work involves the construction of three deep tunnels, 12km in length and up to 165m in depth, which will form a main part of the Hong Kong Harbour Area Treatment Scheme.
The tunnels will collect and convey sewage along the north of Hong Kong Island and under Victoria Harbour to Stonecutters Island for chemical treatment.
The project is due to be completed in 2014.
Hong Kong-based Gammon Construction is 50 per cent owned by Balfour Beatty and 50 per cent by Jardine Matheson, the Asian manufacturing group.