Fourteen months ago, Rupert Murdoch's papers championed Tony Abbott as he headed for election victory to become Australia's prime minister. Yesterday, that mutual admiration came to an abrupt end as the media baron's most influential newspaper labelled him "languishing", "looking flaky" and not "hard enough".

An editorial in The Australian upbraided Mr Abbott for lacking an "authoritative voice" and failing to show "courage and leadership". It said: "Mr Abbott must regroup, trust himself and speak with purpose. Right now his insipid default setting is losing the people."

During the 2013 election campaign, the Murdoch press in Australia was accused of bias by Kevin Rudd, leader of the incumbent Labor Party. An analysis of coverage in Sydney's Daily Telegraph by ABC's Media Watch claimed that, in the first week of the election campaign, half of the paper's 80 stories were slanted against the government, with none against the conservative opposition. Over the next two weeks, it said, 59 stories were against the government, while only four were slanted against the opposition. Just three stories were said to have been in favour of the government.

Australian broadcaster and journalist Mark Colvin described The Australian's attack as a "remarkable turnaround".

"The portents for Mr Abbott as he approaches his second Christmas as prime minister look a lot less promising," he said. "And when, in the same editorial, it asks, 'Is Mr Abbott hard enough?', The Australian has inevitably kindled speculation that Murdoch's editors may have a successor in mind," Mr Colvin added. With two years until the next election, however, any major challenge to Mr Abbott's leadership would be a surprise.

Before Mr Abbott entered politics, he worked as a journalist for The Australian and, to mark the paper's 50th anniversary in July, he described it as Rupert Murdoch's "gift to our nation". Mr Murdoch had previously hailed Mr Abbott as an "admirable, honest, principled man".

The editorial came after the Australian prime minister said that climate change was an "important subject", following talks with the French president François Hollande, last week. He had previously stated that, in his opinion, climate change was "absolute crap".

Mr Abbott had faced pressure to place climate change on the agenda of the recent G20 meetings of world leaders in Brisbane.