SEOUL - North Korean leader Kim Jong Un flew to Singapore on a rented Air China plane, instead of his aged official jet, last June for his first summit with United States President Donald Trump. What he will use to travel to Vietnam's Hanoi for a second meeting with Trump is a point of speculation that will likely remain a mystery until his arrival there.

According to Yonhap news agency, many say Mr Kim is likely to fly on the state jet, codenamed "Chammae-1", this time, because the distance of travel, about 2,760 km, is only slightly more than half of the 4,700 km flown last June, and the Soviet-era jet, even if it is aged, can sufficiently cover the flight.

But others say that Mr Kim could rent a plane from China again if he places a priority on safety.

Some even suggest that he could use his special train to travel all the way to the South-east Asian nation through China for the Feb 27-28 summit, just as he travelled to the neighbouring nation by train last month, noting that Vietnam also has the same rail specifications as North Korea, Yonhap reported.

Mr Kim's grandfather and national founder, Mr Kim Il Sung, travelled by train to Vietnam twice in the 1950s to 1960s, Yonhap said.

The North's state jet, Chammae-1, which is named after the country's national bird of goshawk, is an Ilyushin-62M airliner that can theoretically fly up to about 10,000 km without stopping to refuel. The North's national flag-carrier, Air Koryo, uses the model.

The Chammae-1 was used when the leader's sister, Ms Kim Yo Jong, flew to Seoul to attend the PyeongChang Winter Olympics in February last year. Chairman Kim also used the aircraft when he visited the Chinese city of Dalian for talks with Chinese President Xi Jinping in May last year.

It was also flown to Singapore last June to transport North Korean officials accompanying Mr Kim.

Experts said at the time that Mr Kim chose to fly the rented Chinese plane in apparent consideration of safety. The Air China Boeing 747-400 has reportedly been used by top Chinese officials for overseas trips.

Mr Kim's use of the Chinese plane also underscored the North's reliance on the neighbouring nation, the only country considered to have any meaningful influence over Pyongyang as its main provider of aid and diplomatic support, according to Yonhap.