Sydney: Australian Prime Minister Julia Gillard is heading for a shock defeat at elections on August 21, a new opinion poll showed Saturday, as government infighting and damaging cabinet leaks threatened to derail her campaign.

But Gillard, who is still expected to win by most other opinion polls and political experts, vowed to keep on battling to keep the top job.

"Let's be very clear about this, we're in a fight," she told reporters while campaigning in Perth. "I am going to keep fighting every day of this election campaign."

Defeat for Gillard would sink her plans to slap a 30 per cent tax on iron ore and coal mines, to introduce carbon-trading and to build a $33 billion-plus broadband network.

The latest Nielsen poll reversed a solid lead Gillard's Labour party held in the same poll a week ago. Australia's first female prime minister took over barely five weeks ago from unpopular predecessor Kevin Rudd, who was dumped by his own MPs.

Support for Labour had dived six percentage points to 48 per cent, according to the poll, published on Saturday in The Sydney Morning Herald and The Age newspapers.

It gave the conservative opposition an election-winning 52 per cent, after minor parties are eliminated under Australia's system of transferable voting.

Opinion polls have been erratic but, on balance, they have favoured Gillard. The Reuters Poll Trend, a statistical analysis that aims to smooth out the volatility of differing poll results, shows Gillard winning a slightly increased majority.

The new Nielsen poll shows two-thirds of voters still expect Gillard to win, despite many shifting to opposition leader Tony Abbott, but it will still come as a shock for Labour, which is struggling to heal the wounds of Rudd's dumping.

Abbott yesterday dismissed the latest poll results and said he remained "very much the underdog" in the election.

The new poll, followed leaks of cabinet discussions to newspapers which said they showed Gillard, opposed decisions to boost the state pension and paid paternity leave. If the election mirrors the latest poll results, the opposition would win an additional 28 seats The Sydney Morning Herald said.