Relations between the two superpowers have nosedived in the wake of Pelosi's trip to China's self-ruled neighbour -- which it claims as its territory -- prompting calls from the UN for an urgent de-escalation of tensions.

And Friday saw the environment become the latest victim of the geopolitical jousting, as Beiing said it would withdraw from a series of talks and cooperation agreements with Washington -- most notably on climate change and defence cooperation.

The world's two largest polluters had pledged to work together to accelerate climate action this decade and vowed to meet regularly to tackle the crisis -- a deal that now looks shaky.

Beijing is due to press ahead Saturday with some of its largest-ever military drills around Taiwan -- exercises aimed at practicising a blockade and ultimate invasion of the democratic island, analysts say.

"In the waters around Taiwan island, more than 10 destroyers and escorts of the Eastern Theater Command navy approached from different directions to carry out containment operations," the Chinese army's Eastern Theater Command said in a statement on Friday's drills.

And in a bid to show just how close China's forces have been getting to Taiwan's shores, Beijing's military overnight released a video of an air force pilot filming the island's coastline and mountains from his cockpit.

China's state broadcaster, CCTV, has reported that Chinese missiles have flown directly over Taiwan during the exercises -- a major escalation if confirmed.

But Taipei has remained defiant, insisting it would not be cowed by its "evil neighbour" as it reported Friday that 68 Chinese warplanes and 13 warships had crossed the "median line" that runs down the Taiwan Strait.

- 'Punishing the whole world' -

The scale and intensity of China's drills have triggered outrage in the United States and other democracies, with the White House summoning China's ambassador to Washington on Friday to rebuke him over Beijing's actions.

And Beijing's decision to withdraw from hard-won cooperation on climate change has now sparked wider fears about the future of the planet.

"It's obviously worrying and raises concerns," Alden Meyer, a senior associate at E3G, a climate-focused think tank, told AFP.

It's "impossible to address the climate emergency if the world's number one and number two economies and number one and number two emitters are not taking action," he said.

"And it's always preferable that they do that in a collaborative way."

National Security Council spokesman John Kirby told reporters in Washington the decision was "fundamentally irresponsible."

"They're actually punishing the whole world, because the climate crisis doesn't recognize geographic boundaries and borders," Kirby said.

"The world's largest emitter now is refusing to engage on critical steps necessary to combat the climate crisis."

UN Secretary-General Antonio Guterres warned the two superpowers must continue to work together -- for the world's sake.

"For the secretary-general, there is no way to solve the most pressing problems of all the world without an effective dialogue and cooperation between the two countries," his spokesman Stephane Dujarric said.

- 'The new normal' -

But with tensions over Taiwan having risen to their highest level in nearly 30 years with an elevated risk of military conflict, experts told AFP the latest downturn in relations between the two superpowers could be deep and long-lasting.

"The relationship is in a very bad place right now," said Bonnie Glaser, a China expert at the German Marshall Fund.

The suspension Friday of bilateral military and maritime dialogue while China continues its military exercises was "particularly worrisome," she said.

"We don't know what else they will do," she said. "We just don't know if this is just a temporary thing."

John Culver, a former CIA Asia analyst, said in a discussion hosted by the Center for Strategic and International Studies that Beijing's main purpose with its military exercises was to change that status quo.

"I think that this is the new normal," Culver said.

"The Chinese want to show... that a line has been crossed by the speaker's visit."