Defence Minister Christopher Pyne confirmed his retirement after 26 years in parliament in a statement to the Adelaide Advertiser published late on Friday night.

"It's time to retire while people are asking me to stay, rather than continue and end up later with people telling me to go," he said.

'At fifty one, I still have the opportunity to have a second career beyond politics."

In the two -page statement, the South Australian MP said he was confident the Liberal Party would retain Sturt and government in the coming election.

"The Liberal Party in South Australia and nationally, can be a rambunctious Party at times, but I believe in the party, and always will," he said.

The confirmation comes after much speculation on Friday.

Defence Industry Minister Steve Ciobo also confirmed he will quit at the May election and told The Australian it is time to "do something else".

The prime minister has already lost frontbenchers Kelly O'Dwyer, Michael Keenan and Nigel Scullion, who will retire from parliament at the May poll.

Former foreign minister Julie Bishop, who turned down a role in Mr Morrison's cabinet, will also retire in May.

Mr Morrison was asked if he had spoken to the frontbench pair about their impending decisions, and did not deny Mr Pyne or Mr Ciobo could be about to quit.

"I talk to them all the time," Mr Morrison told reporters in Townsville

"There's a lot of speculation going on, isn't there?"

Mr Morrison also denied he had intervened to defer the pair's announcements until the weekend.

Mr Ciobo told The Australian he was proud to have worked on the Trans-Pacific Partnership and the Indonesian free trade deal when he was trade minister.

"After 17 years in parliament, I have taken the decision that it's time to move on to something else," he said.

Mr Pyne joked about his future with his TV colleague and Labor defence counterpart Richard Marles on the weekly Sky News show they host together.

"Once I decide to announce my retirement, you'll be the first to know," Mr Pyne told his co-host.

Mr Marles praised Mr Pyne for his time in parliament, which began with his election in 1993.

"If it is true, yours has been a mighty career and I for one will miss you. I'll probably get in trouble for saying that, but that's just how I feel," Mr Marles said.

Mr Ciobo will leave his safe Gold Coast seat of Moncrieff, but Peter Dutton's office confirmed he will not seek to leave his marginal seat of Dickson to take the safer spot.

Sky News reported Mr Ciobo would quit his cabinet post before the election, with Mr Pyne temporarily taking on the defence industry role and opening up the potential for another minister to be elevated to cabinet.

Labor leader Bill Shorten said the resignation speculation showed the government had given up.

"I say to Australians, if the ministers in the government are giving up on the government, you should too," he told reporters in Sydney.

Australian Associated Press