Photo/IllutrationIn this Aug. 23, 2015, file photo, an Air New Zealand passenger plane flies past the moon on its way to the Los Angeles International Airport from London, in Whittier, Calif. (AP Photo)

WELLINGTON-- New Zealand's national carrier admitted a registration mistake turned back a flight to China over the weekend, prompting Prime Minister Jacinda Ardern to say Monday that politics were not involved.

She said the incident had no bearing on the relationship between the two nations and she wouldn't be seeking reassurance on that point from Chinese officials.

"I see absolutely no need, given that Air New Zealand have said themselves that they know exactly what the issue was — that they did not meet requirements on behalf of China," she said.

Ardern added, "I think it's important to be really clear and not confuse administrative and regulatory issues as issues to do with the relationship."

In Beijing, foreign ministry spokeswoman Hua Chunying said failure to properly register was a breach of regulations.

"They themselves noted this issue and made a U-turn," Hua told reporters at a daily briefing.

Relations between China and New Zealand have been strained in recent months after New Zealand's spy agency in November halted mobile company Spark from using Huawei equipment in its planned 5G upgrade. The agency said the Chinese company's equipment posed a "significant network security risk."

Under the previous conservative government, New Zealand had fostered much closer ties with China. New Zealand was the first developed nation to sign a free-trade deal with China in 2008, and China has since become New Zealand's largest trading partner.

But New Zealand is also part of the "Five Eyes" security alliance that includes the U.S., Britain, Canada and Australia, which have also expressed concerns about Huawei. And under Ardern, New Zealand has embraced a warmer relationship with Japan.

Since taking office in 2017, Ardern has yet to make a long-promised official visit to meet with Chinese President Xi Jinping.

"Look, I have received an invitation from the Chinese administration to visit," she said Monday. "The outstanding issue simply is a matter of setting dates, and those have not been finalized yet."

Air New Zealand Flight 289 from Auckland to Shanghai was about four-and-a-half or five hours into its journey Sunday when a "technicality" was discovered that meant the plane was not registered in China, the airline said. The flight returned to Auckland.

"We know customers will be deeply disappointed and frustrated by this situation and we are very sorry for the disruption to their travel plans," the airline said. "These customers have now since arrived in Shanghai."

Air New Zealand did not immediately respond to further questions on the incident.