Biden made the comment after visiting a missing-in-action war memorial in his childhood home city of Scranton, Pennsylvania, and putting his hand on the engraved name of Ambrose Finnegan whose plane was shot down and whose body was never recovered.

"He flew single-engine planes, reconnaissance flights over New Guinea. He had volunteered because someone couldn't make it. He got shot down in an area where there were a lot of cannibals in New Guinea at the time," Biden told reporters in Scranton moments after visiting the granite memorial.

"They never recovered his body. But the government went back, when I went down there, and they checked and found some parts of the plane and the like," he said.

Biden again related the story about the man he called "Uncle Bosie" at a separate event as a riposte to the reported comment from Republican presidential candidate Donald Trump that "suckers and losers" die in combat.

Trump has denied making the comment.

Getting emotional when talking about his son Beau, who died in 2015 of brain cancer that the president has connected to his son's military service in Iraq, Biden told the audience of union steelworkers that Trump did not deserve to be commander in chief again.

The comments came at the end of a nostalgic two-day trip to the key battleground state of Pennsylvania for the president as he seeks re-election, including spending 90 minutes at his childhood home in Scranton.

Australian Associated Press