Deputy Prime Minister Winston Peters will become the minister for disarmament and arms control.

In her first foreign policy speech in office, Prime Minister Jacinda Ardern reinstated the Cabinet portfolio of disarmament and arms control.

Ardern announced her deputy Winston Peters would take up the ministerial role.

"The portfolio responsibility will be given to Rt Hon Winston Peters, and is an acknowledgment of the emphasis this government places on our long held anti-nuclear stance, and the role we must play now and in the future," Ardern said to a New Zealand Institute of International Affairs conference on Tuesday morning.

"The pursuit of disarmament is as vital today as it was when Norman Kirk and David Lange proclaimed New Zealand's opposition to nuclear weapons and nuclear testing in the Pacific."

The Labour government of then-Prime Minister David Lange banned nuclear armed and propelled ships from New Zealand waters in the 1980s.

The cabinet position was disestablished by the previous government.

STUFF Then-Prime Minister David Lange holds the nuclear free legislative bill in 1987.

Ardern announced she was also looking at an early ratification of Treaty on the Prohibition of Nuclear Weapons, which New Zealand signed last year.

"At a time when risks to global peace and security are growing and the rules-based system is under such pressure, we must recommit ourselves to the cause of non-proliferation and disarmament, and to the norms and rules which support those endeavours," Ardern said.

"Risks to global peace and security are growing. The greatest challenge we have today comes from North Korea, situated right here in our region."

The speech focused on the importance of allies and the rules based order for small nations like New Zealand.

"Small countries need friends. We will look to strengthen partnerships with long-standing friends who share our values," Ardern said.

In a question and answer session after the speech the prime minister said the biggest threat facing New Zealand was a breakdown in this rules based order.

She also noted real differences with close friendships.

"The real strength of any important relationship lies in its breadth and ability to encompass difference. For example, we were disappointed at the United States withdrawal from the Paris agreement and some of its positioning on trade," Ardern said.

"But our relationship with the US is certainly robust enough to withstand those differences."

She also noted differences with China, while praising them for movement on climate change and trade liberalisation.

"My government will speak honestly and openly with our friends in Beijing. Whether it is about human rights, pursuing our trade interests, or the security and stability of our region."

Ardern said she was eager to begin work on a free trade agreement with the United Kingdom.