'Larger black market' of semi-automatic guns will follow if proposed gun laws come into force, David Seymour suggests

The Prime Minister says any existing black market of semi-automatic weapons in New Zealand won't become larger if tougher gun laws are passed in Parliament.

Jacinda Ardern's comments came as she answered questions from ACT Party leader David Seymour during Parliament's Question Time today.

Mr Seymour asked Ms Ardern if she was "conceding that one of the impacts of her gun law changes may be a larger black market of dangerous semi-automatic weapons outside any regulatory cordon whatsoever?"

"No," Ms Ardern said. "What I'm pointing out is that our gun laws, historically, have been far too relaxed. Am I to take it from the member's question that he's implying that he would rather have us do nothing than do what we are doing today?"

The exchange between the two comes as details around the nationwide gun buyback were released today, as part of the proposed gun law changes that were spurred after the Christchurch terrorist attack that killed 50 people on March 15.

Independent advisors will develop a price list for New Zealand's gun buyback scheme, as new firearms laws are expected to come into force this week. High capacity magazines and parts will be included in compensation to guy owners surrendering their weapons.

Mr Seymour later told 1 NEWS he was concerned by the restriction of compensation "to only those gun owners with appropriate firearms licences".

"If a significant number of weapons aren't handed in, we risk creating a large black market of dangerous weapons without any regulatory oversight. That may be a more dangerous world than we had prior to March 15."

In Question Time today, Mr Seymour asked Ms Ardern if the buy-back changes would be "more successful than those in Australia, which are estimated to have brought back only 40 to 80 percent of the semi-automatic weapons in circulation?"

Ms Ardern said it would be difficult to access the number of military-style semi-automatic weapons and assault rifles that would be handed over during the buyback. 

"Our gun laws as they are mean it is very hard for us to quantify just how many of those weapons precisely are in circulation."

The Third Reading of the gun law reform is set to happen in Parliament today.