US President Donald Trump has agreed to honour America's "One China" policy in a phone call with Chinese president Xi Jinping, the White House said.

Mr Trump had placed the long-standing policy in doubt when he spoke with Taiwan's president in December.

Previous US leaders have followed China's lead in not recognising Taiwan as an independent nation.

The White House said the two leaders discussed a wide range of issues during a lengthy call on Thursday night.

A statement described the call as "extremely cordial" and said the two leaders had invited each other to visit.

The call followed a letter sent by Mr Trump to Mr Xi on Thursday - the president's first direct approach to the Chinese leader.

Mr Trump baited China throughout his campaign, accusing it of unfair trade practices and threatening to challenge its military build up in the South China Sea.

Beijing responded cautiously, expressing "serious concern" about Mr Trump's position on the One China policy and urging the US to maintain close ties with China.

China sees Taiwan as a breakaway province to be reunited with the mainland, by force if necessary. The US cut formal ties with Taiwan in 1979.