National MPs are licking their wounds after suffering one of the worst election defeats in the party's history.

About 20 National MPs lost their jobs last night, including Alfred Ngaro, Tim Macindoe and Jonathan Young.

The resounding defeat has triggered a review into the election campaign and the National Party as a whole, according to leader Judith Collins.

Speaking to supporters last night, she said it was devastating to lose so many National MPs.

"The National Party will take time to reflect and we will review and we will change.

"National will re-emerge from this loss a stronger, disciplined and more connected party."

MPs spoken to by the Herald pointed to a range of factors in the defeat: from the $4 billion "hole" to the leak of an email written by Denise Lee voicing concern about Collins' Auckland Council policy.

Some saw that as the "last straw" for voters, and Collins said it cost them about five points in their internal polls.

"They were just very damaging for us," one MP said.

Many National MPs contacted by the Herald did not respond to request for comment.

Lawrence Yule, who lost the Tukituki seat to Labour's Anna Lorck by just over 700 votes, said he was trying to be philosophical about it, but National's result was "devastating".

"The National Party needs to stand back and look at that. It's been a pretty horrendous couple of years and everybody needs to take stock of that and start building for 2023," he said.

Nicola Willis has made it back in on the party's list – largely because of the high number of electorate seats National lost.

She too said National needed to take stock.

"This is a time we need to stay true to National Party values. If we remember what we are here for, then we remain relevant.

"I think Judith has done an outstanding job in some very trying circumstances and having some stability and looking at how we do better is what is required of us over the next few months. We owe that to our members and supporters."

Coromandel MP Scott Simpson – who won his seat last night – told the Herald that there was "nothing like a horrible, humiliating defeat to focus your thinking".

"I know what a result like this does to a party, to its supporters and to its caucus," he said.

Simpson was on the National Party board in 2002 when it got its lowest result.

"We've got a long road ahead of us in terms of climbing back, but I'm confident we can do that," he said.

Now is not the time to consider issues such as leadership changes, he said.

"But it is time for a pretty serious reflection on what happened, and what needs to be done to change things in the Parliamentary team and the party organisation in the lead up to 2023."

Collins told media she did not expect to be challenged for the leadership.

Mark Mitchell and Simon Bridges have ruled out a run at the top job.

Mitchell told RNZ: "The polls then were showing that we were back in government. I'm not laying all the blame at the feet of the coup [of Bridges], but it certainly helped destabilise us, that's for sure."

MPs will begin heading back to Wellington in the coming days, before a Tuesday morning caucus meeting.

Collins said the result was also a "really big wake-up call for caucus and everyone in the party to be focused on the things that matter for people".

Although he's not out of Parliament, one MP who is considering his future is National's deputy leader Gerry Brownlee.

He told Q&A this morning that he would considering his future over the next few days.

Brownlee entered Parliament in 1996, winning the Christchurch seat of Ilam and has held it ever since.

But last night, he lost it by more than 2000 votes.