Australia PM Abbott faces challenge from Turnbull
Australian PM Tony Abbott is facing a challenge to his leadership from senior cabinet minister Malcolm Turnbull.
The Liberal Party is holding a ballot for the leader and deputy roles.
Mr Abbott told a news conference: "I will be a candidate and I expect to win."
Mr Turnbull, long considered a major challenger to the PM, and Foreign Minister Julie Bishop had earlier asked Mr Abbott to allow the party to hold a leadership contest.
The challenge comes seven months after Mr Abbott survived an internal Liberal challenge to his leadership.
He has since been plagued by poor opinion polls and a hostile upper house.
'Advocacy not slogans'
At a press conference in Canberra, Mr Turnbull earlier said if Mr Abbott remained as leader, the coalition government would lose the next election.
He said he had not taken the decision lightly, but that it was "clear enough that the government is not successful in providing the economic leadership that we need" and that Australia needed a new style of leadership.
"A style of leadership that respects the people's intelligence, that explains these complex issues and then sets out the course of action we believe we should take and makes a case for it.
"We need advocacy not slogans," he said, taking a swipe at Mr Abbott's public habit of repeating phrases such as "stop the boats" numerous times in press conferences.
"If we continue with Mr Abbott as prime minister, it is clear enough what will happen. He will cease to be prime minister and he'll be succeeded by [opposition Labor leader Bill] Shorten."
Analysis: Wendy Frew, Australia Editor, BBC News website
After the leadership debacle that was the previous Labor government, it seemed impossible that the Coalition would be willing to dump Tony Abbott for any pretender.
After being toppled by his deputy Julia Gillard, Labor PM Kevin Rudd seized back his old job in a reverse coup only to lose it forever when the public punished his party at a general election in 2013.
But it seems that at least some in the Coalition government have finally lost patience with Mr Abbott, following a long string of weak public opinion polls, a failure to push any major reforms through the parliament and an inability to stem leaks from his cabinet.
As one unnamed cabinet minister told local media on Monday morning: "This time I think they will get him."
It remains to be seen if Mr Turnbull can muster the numbers to win a ballot against Mr Abbott.
Defence Minister Kevin Andrews, Immigration Minister Peter Dutton and Treasurer Joe Hockey have spoken out in favour of Mr Abbott.
However, Australian broadcaster ABC said that foreign minister and deputy party leader Julie Bishop was expected to be Mr Turnbull's running mate.
Mr Hockey said in a press conference: "The disloyalty of some has been outrageous."
He said only the voting public had the right to change the PM, adding: "We must not become a carbon copy of the Labor Party."
Meanwhile, former long-serving Victorian Premier Jeff Kennett told ABC he was "profoundly disappointed" at Mr Turnbull, calling him "the Kevin Rudd of the Liberal Party".
Who is Malcolm Turnbull?
- Served as Minister for Communications under Mr Abbott, before resigning to launch a leadership challenge
- Many in his party dislike his support for climate change action and gay marriage
- Led the Liberal Party in opposition from 2008-2009 - but lost a leadership challenge to Mr Abbott by one vote
- Previously worked as a successful lawyer and businessman - defending former British spy Peter Wright in the "Spycatcher" case in the 1980s
In his news conference, Mr Turnbull noted the coalition had fared worse than the Labor opposition in 30 public opinion polls by Newspoll in a row.
"It is clear that the people have made up their mind about Mr Abbott's leadership," said Mr Turnbull.
A challenge had been expected later this year, particularly if Mr Abbott's Liberal Party performed poorly at a by-election for the seat of Canning in Western Australia this weekend.