Prime Minister Kevin Rudd vowed to fight until "the last vote is cast" in a rousing speech declaring himself the "comeback kid for Australia" Sunday, one week out from national polls.

Rudd urged the party faithful not to give up hope, despite opinion polls showing the Tony Abbott-led conservatives as clear favourites to win the September 7 election.

"To those who say that Mr Abbott has already won this election, I say this -- never ever, ever underestimate the fighting spirit of the Australian Labor Party," Rudd told the party's major campaign rally in Brisbane.

"I have been in tougher spots before and come back from behind.

"As one young kid said to me the other day -- 'Kevin, we want you to be the comeback kid for Australia'."

Rudd said he would "fight this election until the last vote is cast next Saturday night".

"I believe we can prevail and I believe in the end we will prevail," he said.

Rudd took aim at Abbott's "priorities, judgement and temperament" in his speech, after the opposition leader described the conflict in Syria as "baddies versus baddies" in a television interview Sunday.

The Rudd camp seized on the remarks, made as Australia prepares to assume the rotating presidency of the UN Security Council, as evidence Abbott was not ready for the international stage.

"Can you imagine him at the G20? 'Barack, it's baddies versus baddies'," said Labor Senator Penny Wong.

"I've yet to see a leader of a federal political party wanting to to be PM who would be this embarrassing when it comes to foreign policy."

Opposition spokesman Christopher Pyne later defended the comments, saying Abbott had shown he was "more sophisticated" than Labor because he recognised both sides in Syria were "deeply unpleasant".

The latest opinion polls show the staunch Catholic and social conservative who once trained as a priest on track for a landslide win, with his Liberal-National coalition expected to pick up 86 lower house seats to Rudd's 61.

Despite the numbers both sides are promising a tight race to the finish, with Attorney-General Mark Dreyfus saying there were still large numbers of undecided voters to win over in the final week of campaigning.

But Rudd faces an uphill battle with a public disillusioned by Labor party in-fighting that saw Julia Gillard depose him as leader ahead of the 2010 elections, and he return the favour just weeks before this year's campaign.

It has left him struggling to sell the legacy of Labor's second term, much of which he spent on the backbenches.

Rudd has also allowed gripes about bias from Rupert Murdoch's Australian newspapers to become a distraction and, despite outperforming Abbott in at least two of the campaign's three leaders' debates, has scrabbled for traction.

With the exception of a few gaffes -- the most famous his touting of a political candidate's "sex appeal" as one of her best qualities and a "suppository" faux pas -- Abbott's campaign has hit relatively few snags.

"It's looking very much like it's going to be a coalition victory and the only question now is will it be a substantial coalition victory or will it be a landslide," said Monash University politics analyst Nick Economou, predicting an "absolute whacking".

"So far Labor's been comprehensively outcampaigned by a Liberal party that looks to me as if they've not got out of a trot," Economou told AFP.

"All they've had to do is ensure Abbott stays bolt upright, doesn't say anything too ridiculous, and let Labor hang themselves."