SEOUL — A train believed to be carrying North Korean leader Kim Jong-Il left the northeast Chinese city of Harbin Monday amid speculation he is headed home after a surprise trip to China, a report said.

The secrecy-shrouded visit which began Thursday to the North's chief ally and benefactor is widely seen as seeking Beijing's approval for an eventual transfer of power from the ageing leader to his youngest son Jong-Un.

The train left shortly after 8:00 am (0000 GMT) and was possibly heading for the Tumen River that marks the border with North Korea, South Korea's Yonhap news agency reported.

Kim arrived in Harbin Sunday and stayed near Songhua River before visiting a historic site there linked to his late father Kim Il-Sung, the North's founder, the agency quoted sources as saying.

A source in the city told South Korea's JoongAng Ilbo newspaper that Jong-Un was accompanying his father.

At the city railway station, an employee reached by AFP by telephone said most trains were delayed for one to two hours but she did not know why.

State media in China and North Korea have said nothing about the trip and Kim's next destination is not known. It was unclear whether he may head to a Korean autonomous zone also in northeast China before returning to Pyongyang.

The North's leader reportedly met Chinese President Hu Jintao during an earlier stay in the northeastern city of Changchun.

He is also said to have visited several sites linked to his father, a one-time guerrilla fighter against Japan's 1910-45 colonisation of Korea, in a possible bid to confer legitimacy on another father-to-son succession.

On the first day of his trip on Thursday, Kim visited Jilin's Yuwen Middle School, which Kim Il-Sung attended from 1927 to 1930.

Harbin is also known to be a place where Kim Il-Sung lived for several months to dodge Japanese crackdowns. The city is also known for the 1909 assassination of a senior Japanese official by Korean independence activist Ahn Jung-geun.

On Sunday Pyongyang's state TV station broadcast a programme on Ahn which depicted the assassination as a heroic act, Yonhap reported.

"Kim Jong-Il is making a pilgrimage to all these places to showcase that the upcoming power transfer to Jong-Un is an act of following Kim Il-Sung's legacy," Yang Moo-Jin, of Seoul's University of North Korean Studies, told AFP.

JoongAng Ilbo said his trip to Harbin, the capital of Heilongjiang province, may also be related to the North's chronic food shortage which was worsened by recent floods.

"Most of the rice aid (for North Korea) from China comes from Heilongjiang province," it quoted a source in the city as saying. Harbin is also home to Beidahuang Rice Industry, one of China's biggest rice processing companies.

China is the impoverished North's sole major ally and its economic lifeline. It also chairs six-nation talks on Pyongyang's nuclear disarmament and has been pressing the North to return to the forum after it quit in April 2009.

The current visit is Kim's second to China in about three months, even though he rarely travels abroad. He met Hu during his previous visit in May.

Kim, 68, suffered a stroke in August 2008 and since then has sped up plans for a power transfer in the hardline communist state.