A highlight of Donald Trump's first news conference in months was his striking tale of a brush with death onboard a helicopter alongside former San Francisco mayor Willie Brown.

The only problem? There is no record of any such emergency and the veteran Californian politician says he has never been in a helicopter with Trump.

The Republican ex-president was so caught up in the drama of his story at Thursday's media event that he appeared to have confused the mayor with former California governor Jerry Brown, who once shared an uneventful helicopter ride with Trump.

The Republican presidential nominee claimed to know ex-mayor Brown "pretty well" as he held court in front of a room of journalists at his oceanfront home in south Florida.

"In fact, I went down in a helicopter with him. We thought maybe this is the end. We were in a helicopter going to a certain location together and there was an emergency landing," Trump recounted.

"This was not a pleasant landing, and Willie was... a little concerned."

The story was as startling to Brown, 90, as it was to Trump's audience, given that the Californian says he has never done business with the former president and wouldn't want to be in a helicopter with him.

It quickly became the most talked-about part of the news conference, with the Guardian newspaper branding the anecdote Trump's "chopper whopper."

Brown immediately denied the anecdote, telling the San Francisco Chronicle: "You would have known if I had gone down on a helicopter with Trump."

Once a powerful figure in state politics who was also a speaker in California's legislature, Brown's name had come up because he dated Trump's election rival Kamala Harris for around a year in the 1990s.

Trump said Brown had told him "terrible things" about Harris on the flight and was "not a fan of hers very much at that point."

The other Brown — governor Jerry — did share a helicopter ride with Trump, to the fire-devastated Californian town of Paradise in 2018. Pundits speculated that Trump had mixed the two men up.

But the governor told The Washington Post they had never been in any danger.

"It was a lively ride, but an utterly safe landing," he told the paper, adding that "the subject of Harris never came up."

Brown's successor Gavin Newsom was also on the ride, and said there was no emergency landing, or any other drama, and that Harris was not discussed.