China will "take the gloves off" over Taiwan if required

China is running out of patience with Donald Trump's stance on Taiwan, state media said Monday, and will "take the gloves off" if he keeps challenging the One China policy.

The US president-elect told the Wall Street Journal over the weekend the longstanding policy was up for negotiation, in his latest comment on the issue.

Trump had already irked China by accepting a congratulatory phone call from Taiwanese President Tsai Ing-Wen after he won the presidential election, upending decades of diplomatic precedent in which the US avoided direct public communication with the island's leader.

The foreign ministry, for the second time in two days, warned Trump Monday the One China policy was non-negotiable. Anyone who tries to use it as a bargaining chip will be met with "common opposition" and will ultimately "shoot oneself in the foot", foreign ministry spokeswoman Hua Chunying told a regular briefing.

The China Daily said in an editorial earlier Monday that Trump "will seldom be given the benefit of the doubt twice, because doing the same thing for a third time shows intent". The Taiwan issue is a "Pandora's box of lethal potential", it added.

While the president-elect had been given the benefit of the doubt so far, it said, if he is "determined to use this gambit on taking office, a period of fierce, damaging interactions will be unavoidable as Beijing will have no choice but to take off the gloves."

Trump has threatened to get tough with what he sees as unfair Chinese trade practises and suggested that the One China policy could become a bargaining chip in this.

"Everything is under negotiation, including One China," he told the Journal in the interview published Friday.

Beijing considers Taiwan to be a breakaway province to be brought back within its fold, by force if necessary, and the United States switched diplomatic recognition from Taipei to Beijing in 1979.

China first warned Trump on the issue last month after he said he did not see why Washington must "be bound by a One China policy unless we make a deal with China having to do with other things, including trade". But he has less leverage than he might think, warned the Global Times, a nationalistic tabloid thought to have close ties to hawkish elements of the ruling Communist Party.

China will "mercilessly combat those who advocate Taiwan's independence", it said in an editorial Monday.

If Trump chooses to use the island as a bargaining chip, it added, it "may be sacrificed as a result of this despicable strategy". Taiwan's President Tsai Ing-wen made two stops in the US this month while in transit to diplomatic allies in Central America, despite Beijing's objections.

On her return to the island Sunday she said its "new direction" of diplomacy was clear.

"We must all continue to work to let Taiwan be seen, to let Taiwan make its contribution to the world."