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.

RMS Tahiti was a UK Royal Mail Ship, ocean liner and refrigerated cargo ship. She was launched in 1904 in Scotland as RMS Port Kingston for a subsidiary of Elder Dempster Lines. In 1911 the Union Steamship Company of New Zealand bought her and renamed her Tahiti.