Chatham Islands, island group, 373 sq mi (966 sq km), South Pacific, c.500 mi (800 km) E of New Zealand, to which it belongs. The two largest islands are Chatham Island, which has a large central lagoon, and Pitt Island. The chief town is Waitangi, on Chatham Island. The inhabitants engage mainly in sheep raising and fishing. The islands were explored by Britons in 1791. The native Moriori population was nearly exterminated when Maoris from New Zealand invaded after 1832.