Donald Trump widened his search for Washington's next top diplomat on Sunday, even as he pursued his own unorthodox brand of foreign policy with a Twitter broadside aimed at China.

The US president-elect's senior aide Kellyanne Conway said he would take "a very full slate of meetings" on Monday to fill the remaining cabinet positions, including secretary of state.

America's friends and foes alike are keenly awaiting his choice, hopeful that it will offer clues to the direction US policy will take after he is sworn in on January 20.

Based on Trump's Twitter activity on Sunday, relations with America's top trading partner may be headed for a downturn as he accused Beijing of currency manipulation and military expansionism.

"Did China ask us if it was OK to devalue their currency (making it hard for our companies to compete), heavily tax our products going into their country (the US doesn't tax them) or to build a massive military complex in the middle of the South China Sea?" he demanded, adding: "I don't think so!"

The taunt came two days after Trump risked offending China by accepting a call from the Taiwanese president, and heralded the prospect of a trade battle between the world's largest economies.

China was a frequent target of Trump's during his presidential campaign and every sign points to his taking an aggressive line.

- Trade war threat -
US politicians often accuse China of artificially depressing its currency, the renminbi, in order to boost its exports -- its value has fallen by around 15 percent in the past two-and-half years.

Trump has vowed to declare China a "currency manipulator" on the first day of his presidency, which would oblige the US Treasury to open negotiations with Beijing on allowing the renminbi to rise.

With China holding about a trillion dollars in US government debt, Washington would have little leverage in such talks, but the declaration would harm ties and boost the prospect of a trade war.

Already on Friday, Trump had courted Chinese anger by accepting a congratulatory call from Taiwanese leader Tsai Ing-wen.

China regards self-ruling Taiwan as part of its own territory awaiting reunification, and any US move implying support for independence would gravely offend Beijing.

Trump's incoming vice president, Mike Pence, played down the significance of the call, describing it as a courtesy, and said any new policy on China would be decided after his inauguration.

China responded cautiously to the call, with state media putting it down to Trump's "inexperience."

It is not yet clear whether Trump intends to recruit someone with greater diplomatic experience for the State Department role, but he has run the rule over several high-profile candidates.

Four names have been in circulation for weeks: former New York mayor Rudy Giuliani, former US ambassador to the UN John Bolton, former Republican presidential candidate Mitt Romney and retired army general and ex-CIA chief David Petraeus.

But now more suggestions have begun to emerge.

"It is true that he's broadened the search," Conway told reporters at Trump Tower in New York.

Trump's former campaign manager said the eventual nominee must be ready to "implement and adhere to the president-elect's America First foreign policy, if you will, his view of the world."

Former Utah governor and ambassador to Beijing Jon Huntsman is in the mix, according to CNN, while other reports said Exxon CEO Rex Tillerson and Republican Senator Bob Corker are being considered.

"That list is expanding because... there is not a finite list of finalists," Conway said.

- Petraeus is keen -
Petraeus, who resigned in disgrace as head of the CIA in 2012 after he was caught sharing secrets with his mistress, said he has paid for his mistakes and is ready to work for Trump.

The 64-year-old scholar-warrior, who led the widely-praised "surge" in Iraq from 2008 to 2010, has a depth of experience in world affairs unmatched by the other known candidates.

In 2015 he pleaded guilty to a misdemeanor charge of mishandling classified materials after sharing Afghan war logs with his lover, and was put on two years' probation and fined $100,000.

Pence praised Petraeus as "an American hero" on NBC's "Meet the Press," adding that he "made mistakes and he paid for his mistakes."

Trump "will factor the totality of general Petraeus's career in making this decision," Pence said.