SYDNEY, Australia–Australian police are investigating claims Taylor Swift's father -- nicknamed "Papa Swift" by her adoring fans -- punched a photographer while disembarking a superyacht in the early hours of Tuesday morning.

"Police have been told a 71-year-old man allegedly assaulted a 51-year-old man at Neutral Bay Wharf about 2:30 am, before leaving the location," police spokeswoman Alicia McCumstie told AFP.

Australian police do not formally identify suspects.

However, the alleged victim -- veteran photographer Ben McDonald -- and a law enforcement source both identified the man accused as Swift's father, Scott.

McDonald said he had been taking pictures of the US pop star and her entourage on a luxury superyacht in Sydney Harbour -- an apparent late-night celebration after the last of her four sellout gigs in the city.

McDonald alleges that her security detail put an umbrella in his face to prevent photographs as Swift and the group disembarked and walked down the jetty to a waiting vehicle.

He also claimed an older man confronted him and "took it further" after Swift departed.

"He punched me in the chops," McDonald told AFP. "It was a shock. That's never happened to me in 26 years."

"I didn't know who he was," the photographer said, adding that he initially believed it may have been an overzealous local security contractor "trying to impress the Americans".

"But I looked at photos and saw him holding hands with Taylor, and it was her dad," he said.

Police later said Scott Swift "has left the country" but said inquiries were continuing.

- 'Free Scott Swift' -

A spokesperson for Taylor Swift did not comment directly on Scott Swift's role in the incident.

However, the representative made counter-allegations of pushing and aggression by unidentified people at the waterside.

"Two individuals were aggressively pushing their way towards Taylor, grabbing at her security personnel, and threatening to throw a female staff member into the water," the spokesperson told AFP.

No further details of the incident were offered.

Taylor Swift is on her blockbuster worldwide Eras Tour, which is expected to be the highest-grossing musical tour of all time at more than $1 billion, according to Pollstar.

She has left Australia for Singapore, where she will play to more than 300,000 fans during six sold-out dates at the National Stadium.

Online, Swift fans rushed to her father's defence. "Free Scott Swift," posted social media user @Soyytv.

"Papa Swift", as he is affectionately known, has become a fan favourite, handing out sandwiches, fruit, guitar picks and VIP passes to young members of his daughter's audiences.

After a career as a financial adviser, Scott Swift is now a regular at his daughter's gigs and public appearances -- including this month's Super Bowl in Las Vegas.