The Victorian and NSW Nationals senators due to face the voters at the 2028 election will struggle to hold their seats if the former partners do not re-form the Coalition before then.

Under usual Coalition arrangements, Bridget McKenzie, from Victoria, and Ross Cadell, from NSW, would have been set to be number two on the joint Senate ticket in their respective states. This would have assured them of re-election.

But if they have to run on separate Nationals Senate tickets, it will be hard for them to garner enough votes to be re-elected. One reason is the Nationals would not have candidates in urban lower house seats, and so their Senate how-to-vote tickets wouldn't be handed out in those areas.

As Liberals reeled after the Nationals' sudden desertion of the Coalition on Tuesday, Opposition Leader Sussan Ley is working on her all-Liberal opposition frontbench, to be announced Thursday or Friday.

Senior Victorian Liberal Dan Tehan said: "We're all still in a state of shock of the outcome. I don't think people have really come to terms with it."

Nationals MP Darren Chester, from Victoria, urged negotiations between the parties to continue. He warned "if we go to the next sitting of parliament being two divided party rooms we are giving a free pass to the prime minister".

Nationals leader David Littleproud continued to defend his party's shock decision to split the Coalition.

He told the ABC "plenty of political commentators" were taking potshots.

"Well, good luck, they don't understand what it is to be a Nat. What it is to live and to know and to hear the stories of people who are in danger because of mobile phone towers. Young families that can't afford their mortgage because they can't go back to work, because they can't find a childcare place, because there are none."

Asked if the Nationals were prepared to stay on the backbench indefinitely if the Liberals didn't meet their demands, Littleproud said, "Well, if we get to a juncture after the next election where we can form a government with the Liberal Party, then obviously we're going to support the Liberal Party. But there will be conditions, and the conditions are about those things that are core to making the lives of those people that we represent better".

Former prime minister Tony Abbott joined John Howard in urging an early rapprochement. Abbott said, "I deeply regret the Coalition split and hope that it can be re-formed as soon as possible. History shows that the Liberals and the Nationals win together and fail separately." On Tuesday  Howard warned of the negative consequences of the split.

Liberal deputy leader Ted O'Brien said the Nationals' decision was "more than disappointing".

He said the parties were "stronger together" and he hoped over time the Nationals will "draw the same conclusion that we are better together than we are apart".

With three-cornered contests one issue now the parties are not in coalition, McKenzie was asked whether she would be relaxed about the Liberals running in all Nationals seats.

"This is one of the serious risks of the decision we took yesterday," she said, adding it had been "part of our thinking as went forward".

"We also see it as an opportunity to put a very strong proposition for rural and regional Australia to those communities.

"At the end of the day, though, Coalition arrangements are matters for our state parties - so the LNP in Queensland, the NSW state Nationals and also the Victorian Nationals."