Karkar Island is an oval-shaped volcanic island located in the Bismarck Sea, about 30 kilometres off the north coast of mainland Papua New Guinea in Madang Province, from which it is separated by the Isumrud Strait. The island is about 25 km in length and 19 km in width. In the centre is an active volcano with two nested calderas.

The Bismarck Sea lies in the southwestern Pacific Ocean within the nation of Papua New Guinea. It is located northeast of the island of New Guinea and south of the Bismarck Archipelago. It has coastlines in districts of the Islands Region, Momase Region, and Papua Region.