BEIJING (AFP) - Chinese media warned Mr Donald Trump on Monday (Dec 12) that the one-China policy is "non-negotiable" and dropping it could lead to Beijing supporting US enemies, after the President-elect said he might do so unless Beijing made concessions.

"The one-China policy cannot be traded," an unsigned online commentary in the nationalistic Global Times said, calling Mr Trump "as ignorant of diplomacy as a child".

It warned that if the US openly supports Taiwan's independence and ramps up arms sales to the democratically self-ruled island, China could aid "forces hostile to the US".

"Why couldn't we publicly support them, or secretly sell arms to them?" it demanded.

The Chinese-language commentary was in response to Mr Trump's remark in a Fox News interview on Sunday that he did not see why the US must "be bound by a one-China policy unless we make a deal with China having to do with other things, including trade".

He vehemently defended taking a call earlier this month from Ms Tsai Ing-wen, the leader of Taiwan, which Beijing considers a renegade province.

Although the United States is Taiwan's main ally and arms supplier, it has not had official diplomatic relations with Taiwan since 1979, when it switched recognition from Taipei to Beijing.

The Global Times commentary sounded a more openly menacing tone than previous state media responses, which had largely blamed Taiwan for the phone call and advocated a wait-and-see response.

But this time it warned that if Mr Trump "openly abandons the one-China policy, there will be a real storm. At that point, what need does mainland China have for prioritising peaceful unification with Taiwan over retaking the island by military force?"

The English-language edition of the Global Times quoted a Chinese scholar calling Mr Trump a "novice" in diplomacy with a "very superficial" understanding of Taiwan and Sino-US relations.

"As a businessman, he thinks it's quite normal to do business, but he hasn't realised that the Taiwan question is not a business to China. The Taiwan question is not negotiable," it quoted Professor Li Haidong from China Foreign Affairs University as saying.

But the professor cautioned it was "too early" to conclude if Mr Trump intends to follow through on his threats.

"He's very fickle as well, he may eat his words sometime soon."