SEOUL, South Korea - North Korean leader Kim Jong Il was believed to be making a rare trip to China on Monday aboard his personal armoured train, South Korean news reports said.

Kim's train arrived early Monday in the Chinese border town of Dandong, where some 200 Chinese soldiers and police had blocked traffic and access to the area, South Korea's Yonhap news agency reported from the border.

Kim, who rarely travels abroad but had been rumoured to be planning a trip to neighbouring China, was believed to be on board, Yonhap said.

Officials at South Korea's Unification Ministry and National Intelligence Service said they could not immediately confirm Kim's reported trip.

Kim's visit to China has been a focus of intense attention in recent months, with six-nation nuclear disarmament talks stalled for a year and tensions rising over the sinking of a South Korean naval ship in late March.

Kim, following through on Chinese President Hu Jintao's invitation last year to visit China, was expected to ask Beijing for financial help as Pyongyang copes with an economic crisis at home.

North Korea quit the disarmament-for-aid talks and conducted a second nuclear test last year, drawing tightened U.N. sanctions. China is North Korea's last ally and biggest aid provider and is widely seen as the country with the most clout with its communist neighbour.

The trip would be Kim's first to China since 2006, and his first since reportedly suffering a stroke in August 2008. Kim, who turned 68 in February, is believed to be grooming his youngest son, Kim Jong Un, to succeed him as leader of the nation of 24 million.

The train was heading to the eastern Chinese city of Dalian and will likely travel on to Beijing, Yonhap reported, citing unidentified diplomatic sources in Dandong and Beijing.

The Seoul broadcaster YTN carried a similar report.

Kim's visit also takes place as South Korea investigates the deadly sinking of a South Korean warship near the tense maritime border with the North.

South Korea has not directly blamed its Cold War-era rival and North Korea has denied involvement, but suspicion has focused on Pyongyang, given its history of provocations and attacks on the South.

Seoul officials have vowed retaliation against the culprits behind the March 26 tragedy that killed 46 sailors in one of the country's worst naval disasters.

The two Koreas remain locked in a state of war because their three-year conflict ended in a truce in 1953, not a peace treaty.

The South Korean warship went down near the spot where the Koreas' navies have fought three bloody sea battles since 1999. North Korea disputes the maritime border drawn by the United Nations.