The Greycliffe disaster occurred in Sydney Harbour (Australia) on 3 November 1927 when the harbour ferry Greycliffe and the Union Steamship Company mail steamer Tahiti collided. The smaller ferry was cut in two and sank with the loss of 40 lives, the deadliest incident on Sydney Harbour.
Greycliffe left Circular Quay, Sydney's main ferry terminus, at 4.15pm on Thursday 3 November 1927, with 120 passengers on board, including many schoolchildren returning home. The ferry stopped at Garden Island to pick up dock workers, and then resumed its journey on a course that would have taken it just north of the lighthouse near Shark Island. Its remaining intended stops were to be Nielsen Park, Parsley Bay, Central Wharf (near The Crescent), and Watsons Bay. On roughly the same course, however, was the liner operated by the Union Steamship Company of New Zealand's outward-bound trans-Pacific Royal Mail Ship 7,585 ton RMS Tahiti, three times the size of Greycliffe. Greycliffe was ahead and to the right of the Tahiti.