MAJURO, Marshall Islands (AFP) - A German diver has died exploring the Pacific's famed Bikini Atoll, officials said Wednesday, the first visitor fatality at the former nuclear test site since it opened to tourists in 1996.

The 75-year-old, believed to be from Berlin, was diving at a World War II wreck on Monday when he became separated from his group, local dive master Martin Daly said.

Searchers at the atoll in the northern Marshall Islands found the man's body on Tuesday on the lagoon floor near the hull of the aircraft carrier USS Saratoga.

He said it appeared the man suffered "a medical incident of some sort, possibly a heart attack or stroke". His tanks were 75 percent full of air when they were recovered.

Bikini local government liaison Jack Niedenthal said it was the first time a diver had died there since the atoll began promoting itself as a dive and tourism destination 19 years ago.

Bikini was the site of 24 American nuclear tests in the 1940s and 1950s, including one that sank a fleet of US and Japanese navy vessels.

Among those vessels in the "Baker" nuclear test in 1946 were the Saratoga and the Japanese battleship Nagato, which was the flagship for Admiral Isoroku Yamamoto during World War II.

Bikini Atoll was declared a World Heritage site in 2010.