If it looks like a stretched NZR DE class, it may be because it was a shunter (switcher) built by English Electric, albeit at the Rocklea plant in Queensland rather than in Preston, England.
Only two examples of the G class were built: G50 (in the pic) and 51, both for the Midland Railway of Western Australia in 1963, which was taken over the following year by the WAGR.
G51 was scrapped in 1991, G50 was withdrawn in March that year and preserved by the Australian Railway Historical Society. It is on loan to the Hotham Valley Railway.
It is a Co-Co type with the prime mover an English Electric 8SVT (4 stroke, 8 cylinder) rated at 1,000 hp.