The Prime Minister has brushed aside the resignations of two more senior ministers, insisting the Coalition can still win the federal election in May.

Key points: Christopher Pyne says it's time for renewal and still believes the Coalition can win the election

Christopher Pyne says it's time for renewal and still believes the Coalition can win the election Defence Industry Minister Steve Ciobo told the Prime Minister of his resignation weeks ago

Defence Industry Minister Steve Ciobo told the Prime Minister of his resignation weeks ago Linda Reynolds will be promoted to Defence Industry Minister

Defence Minister Christopher Pyne and his junior minister Steve Ciobo announced on Saturday they will not recontest their seats, adding to a swathe of senior Government figures departing politics.

The rump of resignations presents a political headache for Scott Morrison and the Coalition, which needs to win seats to stay in power after the poll.

"I don't get flapped by things like this, I just keep on going," Mr Morrison told reporters at Parliament House.

Saturday's resignations come after similar announcements from Nigel Scullion, Michael Keenan, Kelly O'Dwyer, and former foreign minister Julie Bishop.

Christopher Pyne is expected to quit federal politics after more than two decades as a Liberal MP. ( ABC News: Matt Roberts )

Mr Morrison has rejected claims a mass exodus of ministers would damage his re-election chances, arguing "personalities will change from time to time".

Mr Pyne, who has spent 26 years in Federal Parliament and is the Coalition's chief tactician, said it was time for renewal in his seat of Sturt.

"Twenty-seven years ago I was preselected as the Liberal candidate on a platform of renewal – in 2019, it is time to renew again," Mr Pyne said.

"You've got to know when to go and it's nice to go when people are asking you to stay, rather than when they're trying to plot to remove you."

Defence Industry Minister Mr Ciobo said he told the Prime Minister about his resignation plans weeks ago.

He said had he been elected deputy leader of the party at the leadership spill last year, he may have stayed in Federal Parliament.

Resignations trigger reshuffle

Saturday's resignations have led to Liberal senator Linda Reynolds being promoted to Cabinet as Defence Industry Minister, a meteoric rise after being elected just five years ago.

Mr Ciobo said he told the Prime Minister about his resignation plans weeks ago. ( ABC News: Jennifer Huxley )

Mr Morrison said Senator Reynolds has had an extraordinary career and her promotion would increase the number of women in Cabinet to seven.

"[That's] the highest number of women ever in an Australian Cabinet, which will be continued under my Government," Mr Morrison said.

Senator Reynolds is a Brigadier in the Australian Army and has been serving as assistant minister for Home Affairs.

Mr Pyne will remain as Defence Minister and Leader of the Government in the House of Representatives until the election.

"We are dealing with some quite sensitive issues presently in the Defence portfolio and I think for the sake of continuity ... it is a very wise and responsible thing for him to continue on," Mr Morrison said.

"Yes, we could have appointed Linda to that role today, but I think the responsible thing is to do exactly what I have done in this case."

Senator Reynolds said her promotion showed that quotas were not necessary in the Liberal Party.

"If you are good enough, you will get in," she said.

"I have been appointed not because of my gender, but because of my experience."

The Liberal Party has only 19 per cent female members, while the ALP has 42.

Senior Liberal figures acknowledge the party must boost the number of women within its ranks to reflect the broader community.

'A stampede for the exit': Labor

Federal Labor has argued the series of resignations show senior Coalition ministers do not believe they can win the upcoming election.

"What will the Morrison Government be remembered for? A stampede for the exit and jobs for their mates," Senator Penny Wong said.

"This lot have actually given up governing."

Mr Pyne said he was confident the Coalition would win the election and his seat of Sturt.

"I'm not leaving because I'm worried about going into opposition, I'm leaving because 26 years is a tremendous run," he said.

Senator Wong said Mr Pyne "could be very charming", but Labor had not decided whether to run in his seat.

"As one of the few moderates in the Parliament ... on a whole range of social policy issues [he] was prepared to occasionally work with Labor to do the right thing," Senator Wong said.

Mr Pyne's state colleague, Simon Birmingham, said his personal attributes would also be missed in Parliament.

"Christopher is renowned for his sharp wit, amazing sense of humour, and incredible verve," Senator Birmingham said.