The visit to China was Kim's first known trip outside North Korea since he assumed power in 2011.
ADVERTISEMENTIn a tweet US President Donald Trump has given an upbeat response to North Korean President Kim Jong-un's surprise train trip to China after being told talks there had gone very well.
He later added that denuclearisation of the Korean peninsular was now a possibility but stressed that sanctions have to be maintained.
"We are going to be cautiously optimistic, but we feel like things are moving in the right direction, and that the meeting yesterday was a good indication that the maximum campaign pressure has been working," Whitehouse Press Secretary Sarah Sanders said.
The visit was Kim's first known trip outside North Korea since he assumed power in 2011 and is believed by analysts to serve as preparation for upcoming summits with South Korea and the United States.
Like his father before him, Kim chose to avoid flying and took his slow but bulletproof train to Beijing instead.
But while Trump is hoping for progress, experts have raised concerns over increased activity at a North Korean nuclear site.
Satellite imagery suggests the North has possibly brought a reactor back online which could be used to produce the fissile materials needed for nuclear bombs.
North Korea insists the reactor is intended to produce electricity for civilian use.