A Kiwi expert on China's foreign relations says a suspected spy balloon shot down over the US was "similar" to one previously publicly demonstrated around Ashburton.

On Sunday, the US military said it shot down a suspected Chinese spy balloon off the Carolina coast after it traversed sensitive military sites across North America.

University of Canterbury professor Anne-Marie Brady told Breakfast that the use of the balloon appeared to be a way to "probe" the US' reaction — as much as it could've been used to gather intelligence.

"What China is doing here is like a probe — it's testing your defences, it's testing your response," she said.

Brady is a globally-recognised academic on China's foreign influence campaigns.

She said there were reports that similar balloons had been used over US military bases in Guam and Hawaii — alongside Japan and the Philippines.

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She said the use of the balloons could be used as a "kind of psychological warfare" — while China has strenuously denied their use as a military tool.

"It's possible to detect these balloons, obviously, so it could be discovered, and the other ones were discovered. But previously, the US government didn't publicly react.

"We don't know what they said privately to China," she said.

Brady said that she had been "very surprised" by the information that the US was now willing to disclose.

"It's really remarkable what has happened — the level of information from the US has been extraordinary. It's really a confrontation, but it's a pushing back on China's behaviour."

China has said publicly that it reserved the right to "take further action" and that the US's shootdown was "an obvious overreaction and serious violation of international practice".

It said the balloon was merely a weather research "airship" that had been blown off course — a claim quickly rejected by the US, who said it had surveillance capabilities and was manoeuvrable. Brady said the country's denials were "predictable".

Previous reports of alleged overflights stretched back past the current Biden administration. Brady said it was "interesting" that former president Donald Trump's administration did not publicly denounce the balloons.

"It's interesting that it's the Biden administration, not the Trump administration — who was famous for being very antagonistic — who had called out China. And said publicly what was happening, and then shot down the surveillance balloon," she said.

The presence of the balloon appeared to prompt the US Secretary of State Antony Blinken to abruptly cancel a high-stakes Beijing visit aimed at easing tensions.

A spokesperson for the Ministry of Foreign Affairs and Trade told 1News yesterday that it "acknowledges it is in New Zealand's interests that the US/China relationship is managed in a way that reduces friction."

"There are still a lot of questions to be answered, but we understand US concerns regarding this incident," they said.

Meanwhile, Brady said the balloon spotted in the US could've been similar to a device tested in public around Ashburton in 2016.

"We had in New Zealand in 2016 — a company...who does a lot of work for the People's Liberation Army, the Chinese army.

"They trialled a similar balloon from a farm in Ashburton...and so we were briefly involved in trying out this kind of technology — because New Zealand is good for near space.

"It's an area of space that is regarded as extremely useful and important for the military these days," she said.