North Korean leader Kim Jong-un appears to be en route to Singapore, either flying directly on his personal Ilyushin-62M jet, or on an Air China 747 that departed Pyongyang this morning (local time).

Mr Kim's Soviet-era Russian plane was briefly spotted on flight tracking websites this morning before disappearing once in Chinese airspace, according to North Korean monitoring website NK News.

In an unusual move this morning, another plane — an Air China 747 — left Beijing at 4:18am to Pyongyang, where it spent about an hour on the tarmac before taking off.

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Initially the flight appeared destined for Beijing, but according to flight tracking data it changed its flight number as it flew past the Chinese capital and is due to arrive in Singapore in the early afternoon.

The flight follows the path of an Air China Airbus A330 that departed Pyongyang yesterday to Singapore — maintaining a route over Chinese territory for as long as possible.

Neither North Korea nor China have revealed details of how Kim Jong-un is travelling to Singapore, but Singapore's Ministry of Foreign Affairs says Mr Kim is due to meet the island-state's Prime Minister Lee Hsien Loong later on Sunday.

Separately a North Korean cargo plane that accompanied Kim Jong-un's plane on his visit to Dalian in May has reportedly been tracked refuelling in China's southern Guangdong province before continuing on to Singapore.

There has also been speculation that Chinese fighter jets would escort Mr Kim's flight while over Chinese airspace, although this hasn't been confirmed by authorities in Beijing.

Kim Jong-un's private Ilyushin jet is capable of flying directly to Singapore depending on its load.

He previously flew on it during his visit in May to the Chinese coastal city of Dalian.

The use of two Air China aircraft to fly North Korean officials — and possibly Mr Kim — also underlines the strength of the traditional alliance between the socialist neighbours ahead of the historic summit.

US President Donald Trump is due to touch down in Singapore on Air Force One on Sunday evening and meet Prime Minister Lee on Monday, ahead of Tuesday morning's summit.