Simon Bridges has defended his party's failure to put more restrictions on semi-automatic weapons, saying it's not clear it would have prevented Friday's massacre.
The National-led Government did tighten the rules somewhat in 2017, accepting seven of a cross-party law and order select committee's 20 recommendations on gun control.
But one of the recommendations then-Police Minister Paula Bennett rejected was investigating the creation of a new category of restricted firearms - semi-automatic rifles.
"That was then," Mr Bridges told The AM Show on Monday morning, three days after a gunman shot dead 50 people in Christchurch.
"Everything has changed. Everything has changed. Please don't get me wrong - I'm not saying to you we shouldn't have gun control change. I don't myself know what would have changed this... we had someone who had IEDs in their car."
Another rejected change was requiring police to record firearms' serial numbers upon renewal of licence or inspection.
Like Prime Minister Jacinda Ardern, Mr Bridges says he wants change.
"Change is needed. We know, I know we want to be constructive partners in all of this. I don't know what the Prime Minister and the Government is proposing. I want to see that... I think there is a wider - I hate the word - conversation to be had, and reform potentially."
So far he's only had a brief talk with Ardern. She says the issue will be top of the agenda when Cabinet meets on Monday.
She told The AM Show Police Minister Stuart Nash had already started work on new gun regulation, and the Christchurch tragedy will "expedite" the process.
"There will be many New Zealanders who will be asking right now, how is it and why is it that someone should be able, in New Zealand, to acquire a military-style semi-automatic weapon?"
She wouldn't commit to an outright ban on all semi-automatic weapons at this stage.
The alleged gunman had five firearms in his vehicle during the attack.