His style may be less combative than the defeated Donald Trump, but experts say a Joe Biden presidency will tighten Washington's squeeze on big power rival China over trade, human rights and security.

Rancour and recrimination defined the relationship between the world's two superpowers under four years of Trump, who slapped Chinese goods with tariffs and blamed Beijing for the outbreak of Covid-19.

Biden promises to be more measured in tone and knit back together tattered alliances on the global stage - moves that could carry a sharper geopolitical threat to Beijing.

"Trump adopted a very aggressive China policy... basically trying to push China on every front," Adam Ni, director of China Policy Centre, based in Canberra, Australia.

"With Biden, I think we'll see a more considered approach that's smarter, that's more targeted... that doesn't focus on aggression alone, but considers long-term competition."

The direction of travel in relations between Washington and Beijing is immovable, analysts say, with US politicians of all stripes determined to ensure their country's economic and military supremacy and blunt China's rise.

Biden has promised to unwind Trump's "America First" policy, which rattled allies and rivals alike, and saw the US withdraw from international forums, including the WHO and the Paris climate deal.

The Democrat, who in the days since his election win has touted conciliation and partnership, is likely to mend alliances from Europe to the Asia-Pacific, building a united front against Chinese tech, trade and security ambitions from Taiwan to Huawei.

A Biden presidency will be primed to "deter aggression" by China, said Anthony Blinken, a longtime adviser to the president-elect, during the campaign.

But where Trump was spasmodic - flinging tariffs on Chinese goods one minute and declaring President Xi Jinping his "friend" the next - experts predict a broader challenge to Beijing from the new administration.

"We're likely to see a more coherent and probably more confrontational policy on geopolitical issues," says Evan Resnick, an academic at the S. Rajaratnam School of International Studies, Nanyang Technological University, in Singapore.

"That will probably make the Chinese quite nervous."

Biden was outspoken during his campaign on China's dismal human rights record.

During a Democratic Party primary debate in February, candidate Biden had strong words for China's Xi, rhetoric which may prove hard to retract.

"This is a guy who doesn't have a democratic - with a small d - bone in his body," he said. "This is a guy who is a thug."

The Biden presidential campaign has also referred to the crackdown on the Muslim Uighur minority in China's Xinjiang as a "genocide", provocative language to Beijing with potential ramifications under international law.

And where Trump wavered on China's rights deficit - putting trade ahead of principle - Biden is under pressure to reclaim American moral leadership.

"His team has already labelled China's internment of Uighurs as genocide," says Bonnie Glaser, Senior Adviser for Asia, Director, China Power Project, Center for Strategic and International Studies.

The President-elect, Glaser said, would "likely build on, not reverse" Trump policies toward Hong Kong, which included the end of preferential trade and travel agreements with the territory as Beijing imposed a new security law.

There are, however, immediate opportunities for a re-set.

Biden's first priority is to control the Covid-19 outbreak which has killed nearly 240,000 Americans so far under the chaotic handling of the incumbent Trump.

Inside China, where the virus first emerged and research on a vaccine is making progress, that signals a chance for rapprochement.

Relations could "shift from fierce confrontation to pragmatic cooperation when it comes to fighting the epidemic", an editorial in Beijing's nationalistic Global Times said on Monday.

"Cooperation... may create more clues to reevaluate some problems inherent in China-US relations."

Biden's job is also to restore the brand power of American democracy at home and abroad.

"Our own democracy, when it is weak, when it looks like it is in disarray... is arguably good for China," advisor Blinken said at a Hudson Institute event recently.

"Because our model looks less attractive than it otherwise would."

He has vowed to rejoin the Paris climate accord as soon as he takes office, as part of a green economy drive countering Trump's climate change denial.

That aligns with the strategic imperatives of China, the world's biggest polluter, which has promised to retool its economy into one dynamised by clean energy.

But the unpredictable Trump has until January to further jam up relations between the world's superpowers.

And years of Trump's vituperations and the uncertainty posed by President-elect Biden has left China wary that the new Cold War is nowhere near its end.

"China should not harbor any illusions that Biden's election will ease or bring a reversal to China-US relations," the Global Times said this week.

"US competition... and its guard against China will only intensify." -AFP