South Korean media report up to 3,000 people were killed or injured when two trains loaded with fuel exploded at a North Korean station near the Chinese border.
No information about the apparent disaster has been released by North Korea. The trains reportedly collided in Ryongchon, a densely populated area about 20 kilometers south of the border with China.
Seoul's Yonhap news agency says North Korea declared a state of emergency after Thursday's collision.
The catastrophic explosion is said to have occurred about nine hours after a special Beijing-to-Pyongyang train passed through the same station carrying North Korean leader Kim Jong-il, who had been holding talks in the Chinese capital.
The trains that collided reportedly were carrying petroleum and natural gas.
South Korea's prime minister and acting president, Goh Kun, has expressed his condolences and pledged to provide humanitarian aid to North Korea, if it is needed.
In Washington, State Department spokesman Richard Boucher told reporters the U.S. government does not know enough about the situation to determine whether U.S. assistance might be warranted, or what kind of aid North Korea might require.
Information for this report is provided by AP.