"Meetings are currently taking place concerning Summit, and more. Kim Young Chol, the Vice Chairman of North Korea, heading now to New York. Solid response to my letter, thank you!" Trump wrote in a tweet, hailing the formation of a "great team" for the talks.

General Kim Yong Chol landed at Beijing airport on Tuesday and will journey on to New York the following day after talks with Chinese officials, according to South Korea's Yonhap news agency.

The trip is part of a flurry of diplomacy before the on-again, off-again summit originally scheduled for June 12 in Singapore.

Trump cancelled the talks last week, citing "open hostility" from the North, but since then both sides have dialled down the rhetoric and the process appears to be back on track.

US negotiators, headed by Washington's current ambassador to the Philippines Sung Kim, met North Korean counterparts in the truce village of Panmunjom that divides the two Koreas on Sunday.

The State Department said a separate team of White House officials has headed to Singapore to sort out logistics.

Chung Sung-yoon, an analyst at the Korea Institute for National Unification, said Kim Yong Chol would be the most senior North Korean official to step onto US soil since Vice Marshal Jo Myong Rok met President Bill Clinton in 2000.

The general has long been a right-hand man to North Korea's leader, playing a front-seat role during recent rounds of diplomacy aimed at ending the nuclear stalemate on the Korean peninsula.

He sat next to Trump's daughter Ivanka, who is also a White House aide, during February's closing ceremony for the Winter Olympics in the South Korean resort of Pyeongchang which was a turning point in the nuclear crisis.

He also accompanied Kim Jong Un on both of his recent trips to China to meet President Xi Jinping, and held talks with Secretary of State Mike Pompeo when he travelled to Pyongyang.

"Kim's official counterpart is Pompeo but he may also push for meetings with (National Security Advisor John) Bolton and even Trump if possible," Chung told AFP.

- Controversial figure -

General Kim is a deeply controversial figure in South Korea, where he is blamed for masterminding the 2010 sinking of the navy corvette the Cheonan, which killed 46 sailors, an attack for which North Korea denies responsibility.

From 2009 to 2016 he was also director of North Korea's General Reconnaissance Bureau, the unit tasked with cyber warfare and intelligence gathering.

During that period North Korea ramped up its hacking programmes, including a hugely costly penetration of Sony Pictures.

His journey to the US caps a frenetic few days of meetings between North Korean and American officials.

Japanese broadcaster NHK reported that Kim Chang Son, Kim Jong Un's de facto chief of staff, arrived in Singapore on Monday, showing footage of him at the airport escorted by three bodyguards.

China's state Xinhua news agency also said one of its photographers saw Kim Chang Son leave a hotel in the city-state.

Also on Monday, a US government aircraft carrying a delegation including Joe Hagin, the White House deputy chief of staff for operations, departed from Yokota air base in Japan en route for Singapore, NHK added.

The Washington Post reported that talks inside the Demilitarised Zone would continue this week between US and North Korean officials.

South Korean media broadcast footage of US embassy vehicles, including one carrying Sung Kim, leaving a Seoul hotel on Tuesday but there were no details on whether the convoy was heading back to the DMZ.

If the original date stands, officials have only a fortnight to finalise thorny protocol details such as where in Singapore the talks will take place and how internationally sanctioned North Korean officials will travel there.

The key task is to settle the agenda. The main stumbling block is likely to be the concept of "denuclearisation" -- both sides say they want it, but there is a yawning gap between their definitions.

Washington wants North Korea to quickly give up all its nuclear weapons in a verifiable way in return for sanctions and economic relief.

But analysts believe North Korea will be unwilling to cede its nuclear deterrent unless it is given security guarantees that the US will not try to topple the regime.