WASHINGTON: A huge, high-altitude Chinese balloon sailed across the US on Friday, drawing severe Pentagon accusations of spying on sensitive military sites despite China's firm denials.

Secretary of State Antony Blinken abruptly canceled a high-stakes Beijing trip aimed at easing US-China tensions.

Aside from the government response, fuzzy videos dotted social media as people with binoculars and telephoto lenses tried to find the 'spy balloon' in the sky as it headed southeastward over Kansas and Missouri at 60,000 feet (18,300 meters).

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

The US actually had been tracking the 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, Biden was initially inclined to order the surveillance balloon to be blown out of the sky, and a senior defense official said the US had prepared fighter jets, including F-22s, to shoot it down if ordered.

The officials, who spoke on the condition of anonymity to discuss internal deliberations, said Defense Secretary Lloyd Austin and Gen. Mark Milley, chairman of the Joint Chiefs of Staff, strongly advised Biden against shooting down the balloon, warning that its size — as big as three school 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.

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.

Blinken, who had been due to depart Washington for Beijing late 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.'

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

The development marked a new blow to already strained US-Chinese relations that have been in a downward spiral for years over numerous issues.

Still, US officials maintained that diplomatic channels remain open and Blinken said he remained willing to travel to China 'when conditions allow.'

Spy balloon 'transits' Latin America later Friday, Pentagon spokesman Pat Ryder said: 'We are seeing reports of a balloon transiting Latin America.'

'We now assess it is another Chinese surveillance balloon,' he added, without specifying its exact location.

Moments before Blinken's decision to cancel his trip — aimed at easing tensions between the two countries — China issued a rare statement of regret over the first balloon and blamed winds for pushing what it called a civilian airship into US airspace.

But President Joe Biden's administration described it as a maneuverable 'surveillance balloon.'

With the rival Republican Party already on the offensive, Blinken postponed a two-day visit.

According to the Chinese state news agency Xinhua, Wang said the two discussed the incident 'in a calm and professional manner.'

'China is a responsible country and has always strictly abided by international law,' Xinhua quoted Wang as telling Blinken.

'We do not accept any groundless speculation and hype,' he said, calling both sides to 'avoid misjudgments and manage divergence.'

Blinken would have been the first top US diplomat to visit China since October 2018, signaling a thaw following intense friction under former president Donald Trump.

Last month, Blinken said he would use the trip to help establish 'guardrails' to prevent the relationship from escalating into all-out conflict.