- Video report by ITV News China Correspondent Debi Edward
US President Donald Trump has delivered a sharp warning to North Korea's leader Kim Jong-un during a speech in South Korea.
Mr Trump told the pariah state leader "Do not underestimate us. And do not try us".
"The weapons you are acquiring are not making you safer, they are putting your regime in grave danger," Mr Trump told an audience of South Korean lawmakers, calling on all nations to join forces "to isolate the brutal regime of North Korea".
"The world cannot tolerate the menace of a rogue regime that threatens with nuclear devastation," he said.
In the speech at South Korea's parliament, Mr Trump painted a bleak portrait of life in North Korea, describing citizens as bribing government officials to leave the country just so they can work as slaves.
A year since he was elected President of the United States, Mr Trump contrasted the poverty and desperation to thriving South Korea, home to a long list of top-rated golfers, he noted.
Mr Trump said the US will not allow its cities to be threatened with destruction, and said that, while America "does not seek conflict or confrontation," it will not run from it, either.
"The regime has interpreted America's past restraint as weakness. This would be a fatal miscalculation," he said.
"This is a very different administration than the United States has had in the past."
Mr Trump also said that the US was "completely rebuilding its military" and spending "billions of dollars" on the "newest and finest military equipment" before adding that he wants "peace through strength".
He also called on all nations to downgrade diplomatic and economic ties with the North and fully implement a series of UN Security Council measures, specifically calling out Russia and China, whose leaders he will meet in coming days.
Mr Trump had hoped to carry out an early morning visit to the Korean demilitarized zone (DMZ) between North and South Korea, but his plans were thwarted by heavy fog.
The Marine One helicopter left Seoul at daybreak and flew most of the way to the DMZ, but was forced to turn back after just five minutes due to poor weather conditions.
On Tuesday Mr Trump had signalled a willingness to negotiate with North Korea as he urged the pariah state to "come to the table" and "make a deal" over its nuclear weapons program.
He also said he'd seen "a lot of progress" in dealing with Pyongyang, though he stopped short of saying whether he wanted direct talks.
"It makes sense for North Korea to come to the table and make a deal that is good for the people of North Korea and for the world," Mr Trump said at a news conference with South Korea's president, Moon Jae-in.
He also sounded an optimistic note on disagreements with the North, saying confidently, if vaguely: "Ultimately, it'll all work out."
It was a striking shift in tone for a president who for months had issued increasingly dire threats to answer any hostile North Korean action with "fire and fury."
North Korea has fired more than a dozen missiles this year but none in nearly two months. Analysts caution against reading too much into the pause.
Moon, who has been eager to solidify a friendship with Trump, said he hoped the president's visit would be a turning point in the standoff with North Korea.
Mr Trump, who is on the longest tour of Asia by a US president in 25 years, has landed in Beijing to meet with China President Xi Jinping.
Shortly after his arrival it was announced that US and Chinese companies had signed business deals the two sides say are worth $9 billion (£6.8 billion).
No details of the 19 agreements signed at a ceremony attended by US Commerce Secretary Wilbur Ross were immediately released.
Such contract signings are a fixture of visits by foreign leaders to Beijing and often involve agreements the Chinese side saved for the event to showcase the country's importance as a market.
MrTrump has made narrowing the multibillion-dollar US trade deficit with China a priority of his administration.
While Mr Trump is looking to boost sagging public approval ratings, the Chinese leader enters their meeting on a political high.
The ruling Communist Party added Mr Xi's name to its constitution at a twice-a-decade congress last month, giving him status equal to Mao Zedong, founder of the communist government, and Deng Xiaoping, who launched economic reforms in 1979.
At the congress, Mr Xi promised to open the economy wider but affirmed plans to build up state-owned companies that dominate industries including finance, energy and telecoms.
That, along with plans for government-led development of electric cars and other technology, makes foreign companies worry that Beijing is squeezing them out of promising fields.