By Agence France-Presse
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, which cited diplomatic sources.
The trip is part of a flurry of diplomacy as preparations gather pace for the on-again, off-again summit between US President Donald Trump and North Korea's leader Kim Jong Un in Singapore on June 12.
US negotiators, headed by Washington's current ambassador to the Philippines Sung Kim, met with 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 also headed to Singapore to sort out logistics for the historic meeting.
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 Marshall 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 the closing ceremony of 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.
General Kim, whose official title is vice-chairman of the central committee of North Korea's Workers' Party, has a background in military and civilian intelligence agencies and is a deeply controversial figure in South Korea.
Seoul blames him for masterminding the 2010 sinking of the South Korean navy corvette the Cheonan, which killed 46 sailors, an attack North Korea denies playing any role in.
Relatives of those who died protested his presence at the Winter Olympics earlier this year.
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 that was seen as an attempt to stop the release of an American comedy film poking fun at the Kim Jong Un regime.