SYDNEY: Australian Prime Minister Julia Gillard Saturday denied that her government was in chaos, after the resignation of two of her most senior ministers prompted a cabinet reshuffle ahead of a national election.

Saturday's announcement that the two ministers had quit came only three days after the Labor leader said elections would be held in September, an unusual step in Australia where polls are usually only called a few weeks in advance.

Gillard said Attorney General Nicola Roxon, the first woman in the job and a staunch supporter of the prime minister, and Senate leader Chris Evans, who has at times been acting prime minister, were leaving the cabinet immediately.

But she denied that the move had thrown her coalition government into chaos.

"Why on earth would anybody say that?" Gillard said.

"Number one, I've named the election date, giving people more stability and certainty than they've ever had before," she told reporters in Canberra.

"Number two, I'm here today making what is a very long-planned announcement, having had the opportunity to discuss with both Chris and Nicola their views about their futures during the course of last year."

Gillard said she had known for a year that Evans, who is Minister for Tertiary Education, Skills, Science and Research, and Roxon did not want to stand for re-election and she had waited for the best time to announce this.

"This is the right time to announce this change moving as we are into the parliamentary week," Gillard said.

Roxon, who was health minister for four years before becoming attorney general a year ago, cited her young family as the reason for her departure.

"All of us need to make decisions about the right time to leave and I believe the right time is now," said Roxon, who will sit on the backbench until retiring at the election, meaning there will be no need for a by-election.

Evans said he will retire sooner, once a replacement can be approved for his seat in the Senate, which does not require a by-election as senators are chosen by their party.

Both Roxon and Evans said they were confident Gillard could win the election even though opinion polls suggest the conservative opposition led by Tony Abbott will take power.

The opposition seized on the reshuffle, saying it was a "horror start" to the year for Gillard after a string of controversies, including ex-Labor MP Craig Thomson facing fraud charges.

"It bears the resemblance to a plot from 'Home and Away' rather than an adult government running one of the world's most important democracies and economies," Liberal Party frontbencher Christopher Pyne said.

The reshuffle means former senior barrister Mark Dreyfus will become the next attorney general and Chris Bowen, currently immigration minister, will take on Evans' portfolio when they are sworn in on Monday.

Gillard said Bowen had wanted a new challenge from the demanding immigration role, set to be a key election issue as Australia struggles to stem a record influx of boatpeople seeking asylum, which will now fall to Brendan O'Connor.