The Royal New Zealand Airforce Air Commodore Andy Scott said the P-8A Poseidon aircraft had spotted the potential sanctions busting in the Yellow Sea and East China Sea.

In addition to the "possible ship-to-ship transfer of illicit goods", New Zealand had reported 35 vessels of interest to the United Nations.

"The upholding of international law is critically important for regional security and we are proud of our ability to contribute to this important work," Scott said.

North Korea is subject to multiple United Nations sanctions banning its nuclear weapons development and use of ballistic missile technology, restrictions it has repeatedly flouted.

The New Zealand military has patrolled the Yellow and East China seas since 2018 as part of multilateral efforts to enforce those sanctions.

It said it reported vessels suspected of trafficking refined petroleum to North Korea, as well as exports of commodities such as coal, sand and iron ore used by Pyongyang to fund its nuclear weapons programme.

China this month complained the New Zealand patrols amounted to "disruptive and irresponsible" surveillance in Chinese airspace.

Beijing accused an aircraft of engaging in "close-in reconnaissance and harassment in the airspace" in the Yellow and East China seas.

Wellington dismissed Beijing's complaints.