Foreign aid workers who arrived yesterday at the scene of a deadly train explosion in North Korea described massive devastation: huge craters, twisted railway ties, flattened houses and rubble "everywhere," though there was no sign of the dead or injured who had apparently been removed by North Korean officials. In an unusually frank statement, secretive North Korea blamed the blast yesterday in Ryongchon, a city near China's border, on human error, saying downed power lines ignited a cargo of oil and chemicals. North Korean officials said the explosion at a railway station killed at least 154 people and injured 1,300, Red Cross official Jay Matta said by telephone from a nearby town. Half of the dead were children, killed when their school was destroyed. "There was just rubble everywhere and very large craters in the ground. The buildings around were totally flattened, especially the houses. It's just a mess everywhere," he said. "There were some signs of a fire or a fireball." Buildings in a radius of hundreds of metres were destroyed, while roofs were ripped off others and windows broken up to four kilometres, aid officials said. They said local officials estimated Ryongchon's population at 27,000, though some estimates put the number much higher. The visit followed a rare invitation from the North's Communist government, which relaxed its normally intense secrecy as it pleaded for international help. North Korea, in its first statement on the disaster, said in a dispatch by its state news agency that the explosion was touched off by "electrical contact caused by carelessness during the shunting of wagons loaded with ammonium nitrate fertiliser," which can also be used in explosives and rocket fuel. **PHOTO CAPTION*** Rescuers sift through rubble at the railway station in Ryongchon, North Korea. (AFP/HO-ICRC)