US President Donald Trump on Friday said the Asia-Pacific region was being held hostage by the "twisted fantasies" of North Korean leader Kim Jong-Un, as he called on countries to stand united against Pyongyang.

Trump has embarked on a tour of Asia this week trying to rally regional support for curbing North Korea's nuclear weapons programme, warning that time is running out over the crisis.

"The future of this region and its beautiful people must not be held hostage to a dictator's twisted fantasies of violent conquest and nuclear blackmail," he said during a speech in Vietnam to the annual Asia Pacific Economic Cooperation (APEC) forum.

The region, he added, must "stand united in declaring that every single step the North Korean regime takes toward more weapons is a step it takes into greater and greater danger".

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 Thursday, Trump was in Beijing meeting President Xi Jinping, where he called on China to "act fast" over North Korea.

"China can fix this problem easily and quickly, and I am calling on China and your great president to hopefully work on it very hard," he said.

Washington has also worked in recent months to convince allies across Asia to oppose Pyongyang, an issue that will remain prominent during his two day trip to Vietnam, which is currently hosting a major regional summit.

Alongside Trump, the leaders of Japan, Russia, China and South Korea are also attending the APEC summit.

Trump departed for his first presidential trip to Asia last Friday, with tensions over North Korea’s nuclear and missile threats looming large. Ahead of his arrival, North Korea had ruled out talks and threatened to increase its nuclear arsenal in a fresh warning to Donald Trump’s administration.

The North’s state-run KCNA news agency had said in a commentary that the US should be disabused of the “absurd idea” that Pyongyang would succumb to international sanctions and give up its nuclear weapons, adding that it is in “the final stage for completing nuclear deterrence”.