Donald Trump has become the first sitting US president to set foot in North Korea, stepping over the demilitarised zone to shake hands with Kim Jong-un.

Even after their historic meeting last summer in Singapore, Mr Trump stunned the world when he walked towards Mr Kim, shook hands and greeted him, and then stepped back across a line marking the North Korean border.

Calling it a “great day for the world”, the US president said he would invite his counterpart to the White House, and also claimed Washington and Pyongyang would resume stalled nuclear talks within weeks.

The North Korean leader told the US president: “It’s good to see you again. I didn’t expect to meet you at this place.”

Mr Kim added: “President Trump has just walked across the demarcation line. That has made him the first US president to visit our country”. He said it was “an expression of his willingness to eliminate all the unfortunate past” and described the handshake as an “expression that today is different from yesterday”.

North Korea military parade celebrating nation's 70th anniversary Show all 18 1 /18 North Korea military parade celebrating nation's 70th anniversary North Korea military parade celebrating nation's 70th anniversary Participants wave flowers AFP/Getty North Korea military parade celebrating nation's 70th anniversary North Korea's leader Kim Jong Un (R) waves with China's Chairman of the Standing Committee of the National People's Congress Li Zhanshu (L) from a balcony AFP/Getty North Korea military parade celebrating nation's 70th anniversary Airplanes forming the number 70 fly in formation and fire flares AP North Korea military parade celebrating nation's 70th anniversary North Korean performers dance EPA North Korea military parade celebrating nation's 70th anniversary North Korean military officers applaud near portraits of late North Korean leaders Kim Il Sung and Kim Jong Il AP North Korea military parade celebrating nation's 70th anniversary North Korean tanks roll past AP North Korea military parade celebrating nation's 70th anniversary Participants cheer as they take part in a parade for the 70th anniversary of North Korea's founding day in Pyongyang, North Korea, Sunday, Sept. 9, 2018. North Korea staged a major military parade, huge rallies and will revive its iconic mass games on Sunday to mark its 70th anniversary as a nation. (AP Photo/Ng Han Guan) Ng Han Guan AP North Korea military parade celebrating nation's 70th anniversary Korean People's Army (KPA) soldiers take part AFP/Getty North Korea military parade celebrating nation's 70th anniversary Korean People's Army (KPA) soldiers march AFP/Getty North Korea military parade celebrating nation's 70th anniversary Participants march during a mass rally on Kim Il Sung square in Pyongyang AFP/Getty North Korea military parade celebrating nation's 70th anniversary A girl reacts during a parade AP North Korea military parade celebrating nation's 70th anniversary North Korean leader Kim Jong Un, right, reacts as he chats with China's third highest ranking official, Li Zhanshu AP North Korea military parade celebrating nation's 70th anniversary People carry flags in front of statues of North Korea founder Kim Il Sung (L) and late leader Kim Jong Il Reuters North Korea military parade celebrating nation's 70th anniversary Performers take part in a concert at the Pyongyang Indoor Stadium AFP/Getty North Korea military parade celebrating nation's 70th anniversary North Korean artillery roll past AP North Korea military parade celebrating nation's 70th anniversary Students perform Reuters North Korea military parade celebrating nation's 70th anniversary Soldiers march during a military parade Reuters North Korea military parade celebrating nation's 70th anniversary Participants wave flowers AFP/Getty

The two leaders then walked back over into South Korea for a meeting. Originally supposed to be a brief exchange of pleasantries, the encounter turned into private talks stretching to about 50 minutes.

“I’ll invite him to the White House right now,” said Mr Trump. “A lot of really positive things are happening. Really positive.” He added: “Stepping across that line was a great honour.”

Mr Trump later addressed members of the US military at an American airbase in Osan, just south of Seoul in South Korea. “Everybody was so happy and many people I noticed from Korea were literally in tears, crying,” he told the troops.

Donald Trump, North Korean leader Kim Jong-un and South Korean president Moon Jae-in at the demilitarized zone (Getty) (Getty Images)

Mr Trump also said sanctions against North Korea remained in place following today’s meeting, but he appeared to be leaving open the possibility of scaling them back, saying that “at some point during the negotiation, things can happen”.

The two leaders last met in Hanoi in February, to discuss the lifting of sanctions on North Korea in exchange for curbing its nuclear plans. That meeting came after another historic summit in Singapore last year, when they loosely agreed to “complete denuclearisation” of the Korean Peninsula. But the Hanoi talks ended abruptly without a deal being struck.

There had long been speculation Mr Trump, who has just been in Japan for the G20 summit, would visit the DMZ while in the region. Some wondered whether he may reach out to the North Korean leader, which he did in the form of a tweet on Saturday morning.

The meeting was then scheduled. The North Korean leader said: “I was very surprised to hear about your offer on the tweet and only late in the afternoon I was able to confirm your invitation. I had wanted to meet you again and especially for both Koreas, this place is a sign of unfortunate history of the past.

Donald Trump says he would like to shake hands with Kim Jong-un

“So for our two Koreas to be able to have this opportunity for me to meet you here is very significant. It means that we can feel at ease and meet each other with positive mindsets. I believe that this will have a positive influence in all our discussions in the future.”

According to CNN, Mr Trump said: “When I put out the social media notification, if he didn’t show up, the press was going to make me look very bad.”

Mr Trump said because Mr Kim showed up, they both looked good. “This could be a very historic moment and I guess that’s what it is. I think the relationship that we’ve developed has meant so much to so many people.”

Critics of the president question his willingness to meet with the North Korean leader, and say he risks providing international legitimacy to a dictator with an appalling human rights record while getting nothing in return.

Supporters of his strategy say it has sharply improved relations between the two countries, at a time when Pyongyang has been expanding its nuclear weapon capabilities.

Mr Trump was accompanied to the DMZ by South Korean Moon Jae-in.

Mr Moon praised the two leaders for “being so brave” to hold the meeting and said: “I hope president Trump will go down in history as the president who achieves peace on the Korean Peninsula.”

The US president ended his four-day trip to Asia and boarded Air Force One to return to Washington shortly after 7pm local time, roughly 90 minutes behind schedule.