Australia claim to have picked up another four Olympic swimming medals after international researchers discovered they were wrongly awarded to the United States more than a century ago.

The Australian Olympic Committee (AOC) said on Friday that the four medals won by Francis Gailey at the 1904 Olympic Games in St. Louis were incorrectly credited to the U.S. instead of Australia.

The AOC's official historian, Harry Gordon, said Gailey, who was raised in the Australian state of Queensland, was listed as an American during the St Louis Games because he competed wearing the colours of the Olympic Club of San Francisco.

Gailey won silver medals in the 220 yards, 440 yards and 880 yards and a bronze in the one-mile freestyle at the "Meet me in St Louis" Olympics, which were run as part of the world fair.

"This is a significant discovery because there have always been a lot of doubts about the St. Louis Games," Gordon told Reuters.

"The Games were run as part of the world fair so the records were not properly kept and it was just assumed a lot of the winners were American because they were wearing U.S. colours."

The mistake was recently discovered by a group of international historians and statisticians who have been investigating the nationalities of athletes at the 1900 Paris and 1904 Olympics.

Gordon said the group had discovered dozens of mistakes involving several nations and were in the process of amending the official medals table.

The discovery of Gailey's true nationality will increase Australia's combined total at the Summer Games to 135 gold, 144 silver and 170 bronze.

"There's no question he's an Australian, so the medals will be credited to Australia," Gordon said.

"The researchers have also discovered errors with some of the other nationalities as well, so there's a fair bit of revision being done."

The discovery gives Gailey, who later settled in California and eventually became a U.S. citizen in the 1920s, claims to being one of Australia's greatest Olympic swimmers.

He becomes the only Australian male swimmer to win medals in four individual events at a single Olympics, bettering the three that Daniel Kowalski won at Atlanta in 1996 and Ian Thorpe matched at Athens in 2004.

Shane Gould still holds the record for the most medals by an Australian swimmer at a single Olympics when she won five, including three golds, at Munich in 1972.