China will send a special envoy to North Korea, state media said Wednesday, after US President Donald Trump concluded an Asian tour to rally support against Pyongyang's nuclear threats.

President Xi Jinping's special envoy, Song Tao, is going to North Korea on Friday to discuss the Chinese Communist Party's congress, which took place last month, Xinhua news agency said, without providing more details.

The announcement came a day after the end of Trump's five-nation tour of Asia, including meetings with Xi during which the US leader urged his Chinese counterpart to act fast to rein in North Korea, warning that "time is quickly running out".

The US administration thinks China's economic leverage over North Korea is the key to strong-arming Pyongyang into halting its nuclear weapons and missile programmes.

On Sunday, Trump said Xi stated that "he is upping the sanctions against" North Korea, though China has not announced any new punitive measures.