Kamaishi is located in the Kitakami Mountains of south-central Iwate Prefecture, with the Pacific Ocean to the east. The spectacular, rugged coast of Kamaishi is entirely within the Sanriku Fukkō National Park. There are four large bays, Ōtsuchi Bay in the north, Ryōishi Bay, Kamaishi Bay and Tōni Bay in the south. Each is separated by large, rocky, pine-covered peninsulas which jut out into the Pacific Ocean. Immediately the rocky cliffs develop into hills rising to along the coast and farther inland.