National broadcaster ABC reported that Christopher Pyne, who also serves as Leader of the House for the Liberal government, would step down at the next election, due by mid-May.

ABC said he would make the announcement on Saturday.

Media reports said junior defence minister Steven Ciobo would also announce his retirement at the weekend.

Pyne would become the fourth cabinet member in Prime Minister Scott Morrison's six-month-old government to announce they were quitting politics.

Several backbench Liberal MP's have also announced they won't contest the next election, or will do so as independents.

First elected in 1993, Pyne has held multiple cabinet positions and was seen as the most prominent moderate in the upper ranks of the Liberal party.

Conservatives inside the party ousted centrist prime minister Malcolm Turnbull last August and Morrison has since led the party hard to the right.

It now faces a tough battle to win re-election and the prospect of spending time on the opposition benches appears to have hastened the departure of several MPs.

Those included former foreign minister Julie Bishop, the most prominent woman in the Liberals and the party's deputy leader under Turnbull.

Current polls show the Liberals heading for their worst electoral defeat since 1983 and Australia getting a seventh change of prime minister in ten years.

Opposition leader Bill Shorten leapt on the news as more evidence that the government is in trouble.

"I say to Australians: If the ministers in the government are giving up on the government, you should too" he was quoted by public broadcaster SBS as saying.