No they are an accent of their own, New Zealanders accent sounds very similar, and one interesting thing about the Australian accent it is the same in every part of Australia, no northern , southern or east and western variations, just the same thing all over Australia.
America has dozens of different accents, Juersey, New Yorker, Texan and southern accent, with variations in northern and Californian sounds.
No, far from it. Accents are different from one side of London to the next, like Brooklyn, Boston and Dallas all have their sounds. Down under is far from British speak, but they are both so beautiful to the ears. I hope that this helps.