Barack Obama warns Donald Trump of significant reaction on One-China policy

US President Barack Obama warns Donald Trump that any tinkering with the decades-old One-China policy could invite a "very significant" reaction from Beijing, days after the President-elect questioned the policy's relevance.

"The idea of One China is at the heart of their conception as a nation and so if you are going to spend this understanding, you have to have thought through what the consequences because the Chinese will not treat that the way they will treat some other issues.

"They will not even treat it the way they issue around the South China Sea, where we have had a lot of tensions. This goes to the core of how they see themselves," Obama told reporters at a White House news conference yesterday.

"Their reaction on this issue could end up being very significant. That does not mean that you have to adhere to everything that has been done in the past, but you have to think it through and have planned for potential reactions that they may engage in," Obama said.

He was responding to a question on the recent phone conversation between Trump and the Taiwanese President and the President-elect questioning the relevance of One China Policy.

At the same time, he indicated that Trump could bring in some freshness in foreign policy.

"I think all of our foreign policy should be subject to fresh eyes. I am very proud of the work I have done. I think I am a better president now than when I started. But you know, if you are here for eight years in the bubble, you start seeing things a certain way and you benefit from, the democracy benefits, America benefits from some new perspectives," he said.

Obama said it should be not just the prerogative, but the obligation of a new president to examine everything that has been done and see what makes sense and what does not.

Given the importance of the relationship between the US and China and how much is at stake in terms of the world economy, national security, the US presence in the Asia- Pacific, China's increasing role in global affairs, there is probably no bilateral ties that carry more significance.

And where there is also the potential if that relationship breaks down or goes into full conflict mode that everybody is worse off, he said.

"I think it is fine for him to take a look at it. What I have advised the President-elect is that across the board on foreign policy, you want to make sure that you are doing it in a systematic, deliberate, intentional way," Obama said.