Sources in China's border city of Dandong say a massive explosion occurred at a North Korean railroad station near the Chinese border that may have caused a large number of casualties.

The explosion reportedly happened about 1 p.m. Thursday in Ryongchon, a town 20 kilometers from the Chinese border.

Details, including the exact number of casualties, are sketchy for the moment, as the communist state cut off international telephone lines in an apparent attempt to prevent details of the explosion from leaking out. But the Seoul-based Yonhap News Agency said some 3,000 people may have been killed or injured in the incident.

Yonhap said two fuel trains collided at the North Korean railroad station, igniting a deafening explosion that rained debris in an 8 kilometer radius. As for the cause of the incident, reports in Seoul also said a gas storage facility near the railroad station had exploded.

The explosion is drawing much attention as it happened around nine hours after North Korean leader, Kim Jong-il, had passed through the station via his private train as he returned from China. It was not clear whether the incident was related to Kim's journey.

Ryongchon, the site of the explosion, is a relatively densely populated strategic transportation center.