There were rumors the fuel was a gift from China to Kim and his energy-starved country, Yonhap said.
There was no immediate suggestion the blast was anything other than an accident.
But the explosion came after Kim met China's new leadership during a rare foreign visit to discuss the North's nuclear weapons plans, tentative economic reforms and aid that has in the past included fuel.
North Korea's official media made no mention of the disaster, but earlier Thursday they broke their silence on Kim's three-day trip to Beijing -- strongly suggesting he was safely back in Pyongyang.
International telephone lines to the area appear to have been cut to prevent information about the explosion getting out, Yonhap added.
The North's creaking medical system would be hard pressed to cope with a large number of casualties, but there was no word any international agency or neighboring country had been asked for help.
Jack Kim and Martin Nesirky/Reuters Apr.22.04
