The South Australian backbencher confirmed to Prime Minister Malcolm Turnbull he would quit the Coalition to form a new Australian Conservatives party on Tuesday morning, with an announcement expected in the Senate this afternoon.

Conservative and moderate Liberals attacked Mr Bernardi, including over his failure to attend a Coalition party room meeting on Tuesday, with Defence Industry Minister Christopher Pyne even calling on him to resign from Parliament and stand again.

"Cory Bernardi was elected as a Liberal," he tweeted. "The honourable course is for him to resign his seat and for him to recontest it as an independent."

"Those most hurt by Cory Bernardi are the hundreds of thousands of SA voters who voted Liberal in the Senate only to be let down by him."

Prime Minister Malcolm Turnbull reportedly told the Coalition joint party room that he asked Senator Bernardi how he could justify remaining in the Senate after being elected as a Liberal just months ago.

Mr Turnbull said Senator Bernardi could not answer the question.

Immigration Minister Peter Dutton, a leading conservative voice within the cabinet predicted anger from voters and Liberal rank and file members.

"It is a betrayal when someone leaves... People will be angry and they will be disappointed," he told ABC radio.

"I think people will be angry about any defection, angry about the betrayal of the Liberal Party values."

Mr Dutton said he was confident no other Liberals would leave to join the new conservative party.

"People, if they want to defeat Bill Shorten at the next election, will be united as a Liberal Party to make sure we can stare down that threat.

"People are much more effective inside the tent than outside... in the end the crossbench don't run the country."

The defection has further derailed the government's start to the new parliamentary year and will lead to speculation about Mr Turnbull's leadership.

Deputy Prime Minister and Nationals leader Barnaby Joyce slammed the move.

"I've seen this movie before, that one ends in tears," he said. "I thought that Cory was made of sterner stuff."

"Bravery presides in staying in the party and trying to change the party, not running away because you can't handle the heat of the kitchen."

Trade Minister Steve Ciobo said his former colleague had been unhelpful.

"Many Liberals feel this way, if you look back over Cory's career, with one or two exceptions he's never laid a glove on the Labor Party.

"Every time he's been in the headlines, it's been about criticism of his own party," he said.

Revenue and Financial Services Minister Kelly O'Dwyer said voters would feel betrayed by a defection so close to the election.

"I think anybody who is elected as a Liberal owes a responsibility not only to the people who have pre-selected them but also to the people who voted for them, who placed their trust in them to be a member of a particular political party."

"I think the Australian people have got no tolerance for parliamentarians who are engaged in ego trips or vanity projects. They want to know that parliamentarians who have been sent to Canberra are focused on their interests and focused on the broader national interest."

Treasurer Scott Morrison said he was thinking of South Australian Liberal Party members as Senator Bernardi quits.

"They're the ones he made the promise to, to be a Liberal," Mr Morrison said.

Education Minister Simon Birmingham told the Financial Review Senator Bernardi has betrayed Liberal voters and should resign his seat.

"There is effectively a contract that all of us undertake when we offer ourselves at election. We go to that election on the ballot paper, with not just our names, but also our party affiliation attached to that and that is an enormous guide," he said.

"I don't kid myself into thinking that there are hundreds of thousands of South Australians who know and like Simon Birmingham and choose to vote just for me."

The soon-to-be-former Liberal attracted 2043 first preference votes at the July 2016 double dissolution election, 0.025 per cent of the required quota.

West Australian Liberal Andrew Hastie said Senator Bernardi was a good friend, and the defection would only add to Senate gridlock.

"I wish that he had attended the Liberal Party room meeting this morning, looked us all in the eye and explained his reasons," Mr Hastie wrote on Facebook.

"He was elected as a Liberal Party senator and owes his colleagues an explanation. Party members and voters will be rightly disappointed."

Nationals MP David Gillespie said he was not surprised by the move.

"Cory has always been a man of his own opinion. He's been very forthright in previous governments and this current one," he said.

"As opposed to the other side ... where you get expelled if you don't follow the party line."

WA Liberal Ken Wyatt said he'd like to see Senator Bernardi remain, "but if he's made that decision then I'm not going to begrudge him," he said.

Right-wing backbencher Craig Kelly said his colleague should think again.

"You can do a lot more inside the Liberal Party, working for, arguing those things that you believe in, than actually outside the tent," he said.

South Australian Liberal Sean Edwards said party members expected Liberal MPs to serve out their terms.

"I would prefer to see Senator Bernardi stay within the Liberal Party and do the work that all the members that preselected him in preference to members like myself [expect]," he said.

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