A New Zealand-made Pacific Aerospace P-750 XSTOL was spotted at North Korea's first airshow in October 2016.

New Zealand aircraft manufacturer Pacific Aerospace has pleaded guilty to unlawfully exporting aircraft parts to North Korea.

The Hamilton firm broke both New Zealand law and United Nations sanctions when it indirectly sent aircraft parts to the hermit state in February 2016.

The development comes as tensions continue to rise on the Korea peninsula with US President Donald Trump and North Korean leader Kim Jong Un locked in a war of words over Pyongyang's increasing nuclear capability.

SUPPLIED Pacific Aerospace chief executive Damian Camp with a P-750, the type of plane spotted at a North Korean airshow in October 2016.

The US is trying to strangle North Korea economically through sanctions to give up its nuclear ambitions, while Kim has accused the US of declaring war and threatened to detonate a nuclear device over the Pacific as a demonstration of his country's ability.

Appearing at Manukau District Court on Wednesday, Pacific Aerospace's defence lawyer Emmeline Rushbrook confirmed guilty pleas to three charges for the indirect export of aircraft parts to North Korea.

The company also pleaded guilty to making an erroneous declaration on a customs export form.

KCNA North Korea under Kim Jong Un, second from right, has continued to develop nuclear capabilities.

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* How did a New Zealand-built plane end up at a North Korean air show?

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Both Pacific Aerospace chief executive Damian Camp, present at the hearing, and New Zealand Customs declined to comment after the hearing.

Judge John Bergseng set down sentencing for January 2018.

TOM LEE/STUFF The P-750 XSTOL, called the "Swiss army knife of an aircraft" by its maker, is able to take off on short runways, ascend quickly, and carry heavy loads.

International security expert and Waikato University law professor Al Gillespie said the judge should "throw the book" at the company given the gravity of the international situation.

"I cannot think of a more serious situation on the planet now."

Gillespie said the escalating tension between North Korea and President Trump was at an "absolute knife edge".

REUTERS / KEVIN LAMARQUE U.S. President Donald Trump has called North Korean leader Kim Jung Un a "rocket man".

"In the wider context what [Pacific Aerospace] have done isn't going to make North Korea a bigger nuclear power. But what is significant is the whole international community needs to be shoulder to shoulder right now in applying the toughest possible sanctions to North Korea."

Customs laid the charges after one of Pacific Aerospaces' P-750 XSTOL planes was spotted at the Wonsan Air Festival in North Korea in September 2016.

The direct or indirect supply of aircraft, related parts and aerospace training to North Korea is a violation of UN Security Council Resolution 1718.

TOM LEE/STUFF Hamilton-based Pacific Aerospace is based at the airport.

The 2006 resolution was agreed on by UN member states in response to North Korea testing a nuclear weapon.

Under New Zealand law, a company which breaches a UN-mandated ban can be fined up to $100,000.

A company can be fined up to $5000 for making an erroneous declaration under the Customs and Excise Act.

Previously, Pacific Aerospace chief executive Damian Camp expressed surprise when the P-750 XSTOL plane was sighted at the Wonsan Air Festival.

Aram Pam, a Singaporean-based photographer who attended the airshow and photographed the plane, told Stuff it flew as part of demonstration by the North Korean national airline, Air Koryo​.

A UN Security Council report from February 2017 - written by a panel of experts tasked with investigating sanction breaches - says Pacific Aerospace sold and delivered the P-750 XSTOL aircraft to a Chinese company in September 2015.

The report includes a chain of emails that suggest the company knew one of its planes was in North Korea, and planned to provide parts and engineering training.

The emails, from January 2016, show Pacific Aerospace and its Chinese partner were planning to provide a replacement flap motor, tools and training to fix a problem with the aircraft.

"We are planning for [name redacted] to deliver training on how to replace the flap motor and he will provide the necessary tools for one of the BGAC reassembly team to be able to replace the flap motor in North Korea," an email from Pacific Aerospace to a Chinese counterpart said.

Trump tweeted on Sunday that only "one thing would work" to stop Kim Jong Un's regime from further developing a nuclear arsenal aimed at hitting the U.S. mainland.

While he didn't provide further explanation, it left observers speculating that it might be a military choice and military exercises have stepped up in recent weeks, including a flight of US B1 strategic bombers near North Korea this week.

He's also played down hopes for direct talks between the U.S. and North Korea as touted by his own Secretary of State Rex Tillerson, tweeting that Tillerson was "wasting his time".