China has urged “calm” amid a dispute over a giant Chinese balloon which is sailing high above the US.

The balloon has led to Pentagon accusations of spying on sensitive military sites, despite China’s firm denials, and prompted US secretary of state Antony Blinken to abruptly cancel a high-stakes Beijing trip aimed at easing tensions with China.

Aside from the government response, fuzzy videos dotted social media as people with binoculars tried to find the “spy balloon” in the sky as it headed south-east over Kansas and Missouri at 60,000 feet.

It was spotted earlier over Montana, which is home to one of America’s three nuclear missile silo fields at Malmstrom Air Force Base, defence officials said.

Antony Blinken
Antony Blinken cancelled a trip to China (AP)

Later on Friday, the Pentagon acknowledged reports of a second balloon flying over Latin America.

“We now assess it is another Chinese surveillance balloon,” said brigadier general Pat Ryder, the Pentagon press secretary. He declined to offer further information such as where it was spotted.

The US actually had been tracking the initial balloon since at least Tuesday, when President Joe Biden was first briefed, White House press secretary Karine Jean-Pierre told reporters.

According to three US officials, Mr Biden was initially inclined to order the surveillance balloon to be blown out of the sky, and a senior defence official said the US had prepared fighter jets, including F-22s, to shoot it down if ordered.

The officials said defence secretary Lloyd Austin and general Mark Milley, chairman of the joint chiefs of staff, strongly advised Mr Biden against shooting down the balloon, warning that its size – as big as three buses – and considerable weight could create a debris field large enough to endanger Americans on the ground.

The Pentagon also assessed that after unspecified US measures, the possibility of the balloon uncovering important information was not great.

It was not the first time Chinese surveillance balloons have been tracked over US territory, including at least once during former president Donald Trump’s administration, officials said.

Mr Blinken’s trip cancellation came despite China’s claim that the balloon was merely a weather research “airship” that had blown off course.

The Pentagon rejected that out of hand – as well as China’s contention that the balloon was not being used for surveillance and had only limited navigational ability.

Mr Blinken, who had been due to depart Washington for Beijing on Friday, said he had told senior Chinese diplomat Wang Yi in a phone call that sending the balloon over the US was “an irresponsible act and that (China’s) decision to take this action on the eve of my visit is detrimental to the substantive discussions that we were prepared to have”.

China’s Ministry of Foreign Affairs said in a statement on Saturday morning: “In actuality, the US and China have never announced any visit. The US making any such announcement is their own business, and we respect that.”

According to Beijing, Mr Wang said China “has always strictly followed international law, we do not accept any groundless speculation and hype. Faced with unexpected situations, both parties need to keep calm, communicate in a timely manner, avoid misjudgments and manage differences”.

After passing the sensitive military sites in Montana, the balloon was moving south-east over the heartland of the central United States during the day and was expected to remain in US airspace for several days, officials said.

A high-altitude Chinese balloon sailing across the US
The huge, high-altitude Chinese balloon has been sailing across the US (Anna Griffin/Missourian via AP)

The development dealt a new blow to already strained US-Chinese relations that have been in a downwards spiral for years over numerous issues. Still, US officials maintained that diplomatic channels remain open and Mr Blinken said he remained willing to travel to China “when conditions allow”.

“We continue to believe that having open lines of communication is important,” he said.

A US State Department official said Mr Blinken and deputy secretary of state Wendy Sherman had both protested to the top official at the Chinese Embassy on Wednesday, a day before the Pentagon announced the discovery of the balloon.

Mr Blinken’s long-anticipated meetings with senior Chinese officials had been seen in both countries as a possible way to find some areas of common ground at a time of major disagreements over Taiwan, human rights, China’s claims in the South China Sea, North Korea, Russia’s war in Ukraine, trade policy and climate change.

Although the trip, which was agreed to in November by Mr Biden and Chinese President Xi Jinping at a summit in Indonesia, had not been formally announced, officials in both Beijing and Washington had spoken in recent days about Mr Blinken’s imminent arrival for meetings on Sunday and Monday.

China, which angrily denounces surveillance attempts by the US and others over areas it considers to be its territory and once forced down an American spy plane and held its crew captive on Hainan Island, was relatively conciliatory in its response to the US complaints.

In a statement that approached an apology, the Chinese foreign ministry said the balloon was a civilian airship used mainly for meteorological research. It said said the airship had limited “self-steering” capabilities and had “deviated far from its planned course” because of winds.

“The Chinese side regrets the unintended entry of the airship into US airspace due to force majeure,” the statement said, citing a legal term used to refer to events beyond one’s control.