Up to 3,000 people have been killed or injured in a huge explosion after two fuel trains collided in North Korea, reports say. The blast happened at Ryongchon station, 50km north of Pyongyang, South Korea's YTN television said. The incident reportedly happened nine hours after North Korean leader Kim Jong-il passed through the station on his way home from a visit to Beijing. Mr Kim had been in China to discuss North Korea's nuclear programme. South Korea's Yonhap news agency said the colliding trains were carrying gasoline and gas, and that they crashed at around 1300 local time (0400 GMT). **'Bombardment'*** The report was based on information from unnamed Chinese sources near the border with North Korea, said news agencies. It was not possible to obtain independent confirmation of the number of casualties, as North Korea is notoriously secretive and rarely reports its own accidents. "The station was destroyed as if hit by a bombardment and debris flew high into the sky," Yonhap quoted its sources as saying. The BBC's Kevin Kim in the South Korean capital, Seoul, says there are various theories about the explosion, including speculation that it may have been an assassination attempt against the North Korean leader. However, he says this has been dismissed by the South Korean authorities, who believe it was an accident. **Emergency*** Our correspondent says another theory is that liquefied petroleum gas carried in one of the trains was a gift from China to North Korea after Mr Kim's visit to Beijing. Yonhap said the North Korean authorities had declared a state of emergency in the area and cut off all international telephone lines, apparently to stop news of the accident spreading. The agency quoted a South Korean defence ministry official as confirming that the explosion had taken place. But a Chinese railway worker at the Dandong border crossing, contacted by Reuters news agency, said he had not heard of a blast and had seen no signs of any emergency effort under way.