SYDNEY (AFP) - The man tipped to become Australia's next prime minister pilloried the country's right-wing media on Wednesday (May 8) after an attack about his late mother that has turbocharged an already heated debate about press partisanship.

Decrying a "new low" in Australia's bare-knuckle politics, the usually phlegmatic Labor leader Bill Shorten became emotional as he lashed out at "bloody lazy" journalism and "gotcha sh*t" ahead of the closely fought May 18 election.

Like Britain and the United States - Australia's stridently right-wing media plays a prominent role in political life.

But some experts, like communications professor Tony Walker of La Trobe University, have accused titles owned by mogul Rupert Murdoch of taking a "battering-ram approach" during this febrile campaign season.

"(They) have stepped up the war against the Labor Party since the election was called," he wrote in a recent commentary.

The group's front pages and TV commentaries have echoed and amplified ruling Liberal party campaign messaging that targets Mr Shorten - a former union leader whose party is a few percentage points ahead in the polls.

The confrontation reached a peak on Wednesday when Sydney tabloid The Daily Telegraph accused Mr Shorten of misleading voters about his dead mother's life, in a front-page splash that carried the block-caps headline "Mother of invention."

Mr Shorten had told the story of how his mother had been forced to defer her dreams of being a lawyer to help her family, which the Daily Telegraph suggested was misleading because she did eventually attend the bar in her 50s.

"Who do some people in News Corp - and it's not all the journalists I make that very clear - who do some of these lazy people think they are?" Mr Shorten railed after being asked about the piece, his voice cracking with emotion.

"They play gotcha sh*t about your life story, and more importantly my mum's."

The tabloid is a News Corp Australia publication, a branch of Mr Rupert Murdoch's global media empire which also includes America's influential Fox News and Britain's The Sun.

Daily Telegraph writer Anna Caldwell defended the story, telling Mr Murdoch's Sky News it "in no way, shape, or form was an attack on Bill Shorten's mother".

CHANGING TIMES?

It is not the first spat between Australia's left-leaning leaders and Mr Murdoch's notoriously combative press, but it may prove to be one of the most consequential.

The mogul has occasionally backed leaders from the centre-left - most notably Mr Tony Blair - but only when the political writing was on the wall for conservative contenders.

Even his high-brow titles have become more overtly political over the years, according to Ms Margot Saville, a journalist who joined The Australian as a cadet in 1987.

"It was still very much the paper of record," she said, noting a shift towards more opinion. "It changed a lot."

Similarly, Australia's leftist leaders have usually held their tongue about Mr Murdoch until long after the end of their political life.

Former Australian prime minister Kevin Rudd sought and received his support when running for office, but last year described him as "the greatest cancer on the Australian democracy".

"Murdoch is not just a news organisation. Murdoch operates as a political party, acting in pursuit of clearly defined commercial interests, in addition to his far-right ideological world view," Mr Rudd claimed.

Few would doubt that Mr Shorten's tears were real, but there is also little doubt he seized a political moment.

His response is symbolic of a growing sense among some on Australia's left that Mr Murdoch's once-feared machine has lost touch with mainstream voters and is vulnerable - even as President Donald Trump and Brexit backers reap the rewards of his support.

Mr Shorten is the first leader in decades not to seek Mr Murdoch's endorsement.

Throughout his career, the 51-year-old has often been accused of being bland and uninspiring, but not after his furious attack on News Corp.

"This is certainly not the first time a Labor leader has had a bash at the Murdoch media in a recent campaign," said Dr Michelle Grattan of the University of Canberra.

"But it was probably one of the more effective."