And it all started with a cheap flight.

The 62 year-old man found "bargain" return flights for USD$1,000 (AUD$1,435), a major saving from the usual airfare to Sydney costing USD$3,500 (AUD $5,022).

Kingsley Burnett boarded the flight in New York, hoping to see the sails of the Sydney Opera House in 20 hours' time.

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However, he was shocked when the plane began its descent over the snow-covered peaks of Billings, Montana instead.

"At that point I knew I was in trouble," he told Montana's KTVQ.

He was even more shocked to see the small aircraft to his final destination, Sidney, Montana.

"I saw the little plane with like nine passengers and wondered 'how is that going to get me to Australia,'" Mr Burnett told the New York Post.

The small Cape Air jet was booked to fly Mr Burnett 1 hour and 25 minutes to Sidney, a town with 6,000 inhabitants.

Making the mistake easier to understand, trips to Sydney, Australia and Sidney, USA both take around 20 hours by plane from La Guardia airport, New York.

And the airport codes are similar, S-D-Y instead of Australia's S-Y-D.

"Somebody has to fix that," Mr Burnett told KTVQ.

An American Airlines desk attendant, Carol Castellano, helped Mr Burnett book accommodation overnight in Montana and return flights to New York.

"Montana didn't have kangaroos. It had Carol. And that was good enough for me," he said.

The Montana hotel attendant, where Mr Burnett stayed, was not shocked by the events.

"This is the second time we've had a guest that was trying to get to Sydney, Australia," hotel manager Shelli Mann said.

Mr Burnett missed the launch of a cruise booked from Sydney but has rescheduled his trip for June 2023.