An international flight from Auckland to Shanghai has turned around mid-air and returned to New Zealand, sparking concerns over increasingly frosty relations between the two countries and setting off a political war of words.

Air New Zealand flight NZ289 left Auckland on Sunday morning but, four-and-a-half hours into its trip to Shanghai, the Boeing 787-9 made a U-turn in a move that has been described as “very unusual” by aviation experts.

In a statement Air New Zealand said the plane was new to the company’s fleet, and did not have the correct paperwork allowing it to land in China.

“This issue relates to a particular aircraft which is not yet certified to operate to China but was unfortunately assigned to operate our Shanghai flight on Saturday night,” the spokesperson said.

“Yesterday Air New Zealand was advised that the original application to have this aircraft registered to operate to China had expired and a fresh application was submitted.”

The unorthodox incident has prompted speculation the issue with the plane’s paperwork was due to an error in the airline referring to the city of Taipei as the capital of Taiwan rather than a city in China. New Zealand news website Stuff claimed to have spoken to multiple sources saying the turnback was down to a “reference to Taiwan which China took to be an acknowledgement that the island was independent”.

Air New Zealand did not respond to questions about a Taiwan link but said “as is required, the application includes a list of destinations the airline operates to, including Taipei”.

China has a history of demanding international airlines not refer to Taiwan’s independence or nationhood on its websites or promotional material, and in the past has urged Qantas, Air Canada and others to change how it refers to the island.

John Nicholson, CEO of industry body Aviation New Zealand described the incident as “very unusual”.

“Aviation is a highly regulated market, and China is a highly regulated market and everyone has to do everything by the letter of the law,” he said.

“It gets into the political situation and the way the different governments recognise or don’t recognise states, and I would think Air New Zealand would be guided very much by what the New Zealand government position is … therefore look at it in context of the New Zealand government’s relationship with China.”

Opposition leader Simon Bridges suggested the returned flight was indicative of increasingly tense relations between China and New Zealand. “We need to know what has happened here. Is it part of the ongoing deterioration in relations between this NZ Govt & China?” Bridges tweeted.

Prime minister Jacinda Ardern responded saying “it was wrong” to view the incident as politically motivated.

“In the past New Zealand has enjoyed a consensus approach to foreign policy, a unified front, that’s in New Zealand’s best interests. Them [the opposition National party] spreading misinformation around this flight I see as irresponsible and a real departure on what we’ve experienced on foreign policy before,” Ardern told TVNZ.

“Our relationship with China is a complex relationship, it sometimes will have its challenges, but they remain an incredibly important economic and people-to-people partner.”

Ardern cancelled her first planned state visit in November 2018 because both parties were too busy. She said the two countries “continued to discuss dates” for a visit sometime in 2019.

Relations between the two countries have become increasingly strained in recent months, following a recommendation from New Zealand’s spy agency that the roll-out of 5G by Huawei posed “significant national security risks”.

Subsequently New Zealand telco company Spark said it would not use the company as part of the 5G roll-out, although justice minister Andrew Little has stopped short of calling it a ban.

A major joint tourism event to be unveiled in Wellington between the two countries has also been postponed, with reports that China refused to send any government ministers to attend.

China’s foreign affairs spokesperson Hua Chunying said the Air New Zealand flight had turned around on its own accord. “Due to temporary glitch in dispatchment, this airplane failed to obtain a landing permit with its destination and decided of its own accord to return en route.”