The South Korean reports said the number killed or injured could reach 3,000, but that figure could not be confirmed.
The secretive North Korean government declared a state of emergency, cutting international phone lines in the region in an apparent attempt to block details of the explosion from filtering out, South Korean media reported.
North Korea's ruler, Kim Jong Il, had passed through the area on a specially fitted train only nine hours earlier en route back to the capital, Pyongyang, after a surprise four-day summit in Beijing. The talks were aimed at restarting negotiations to dismantle the North's nuclear weapons programs that have been deadlocked for months. Though the timing of Kim's travel through the area raised speculation that the explosions might have been the result of a failed assassination attempt, US and South Korea officials dismissed this hypothesis as unlikely.
''All indications at the moment are that the cause of the explosion was purely accidental," said one US official.
South Korea's semi-official Yonhap news agency quoted unnamed North Koreans living in China who had spoken to relatives near the explosion site as saying the area looked as if it had been bombed.
''The area around Ryongchon station has turned into ruins as if it were bombarded," Yonhap quoted the witnesses as saying. ''Debris from the explosion soared high into the sky and drifted to Shinuiju," on the border with China.
South Korean media reported that some of the injured were evacuated to hospitals in Dandong, China.
Residents on the Chinese side of the border apparently saw smoke rising from the scene. South Korean officials said North Korean authorities were trying to determine the cause of the accident.
''We have yet to find out the cause of the incident, the kind of explosion, and how many died," said a South Korean Defense Ministry official quoted by Yonhap, speaking on condition of anonymity.
The train station is on North Korea's main rail link to China, built over 60 years ago during the Japanese occupation of the region. ''Besides the human tragedy, this track is one of North Korea's economic lifelines," said Sung Wook Nam, a North Korea specialist at Korea University in Seoul. ''It could take at least a month to rebuild the track itself, but the clean-up of the area, depending on how much spilled chemicals there are, could take six months or a year. The North Koreans are going to need outside help to do that, and the chances are that Kim Jong Il is going to have to ask China for it."
The explosion took place near North Korea's Shinuiju Economic Zone, a region of factories that in the past two years has sought with limited success to spur development with foreign partners.
