Beijing, Dhu-AlHijjah 27, 1437, September 28, 2016, SPA -- An explosion at a coal mine in China which killed 18 people was caused by "illegal mining", according to an initial investigation, local media reported Wednesday, according to dpa. The explosion occurred Tuesday at a small coal mine in the Ningxia Hui autonomous region in north-western China while 20 miners were underground, the Xinhau news agency reported. Excessive gas and the destruction of the mine's shaft were making the rescue difficult, local mayor Wu Yuguo told Xinhua. Two miners were still missing and the owners of the mine were in police custody, Xinhua reported. --SPA 13:26 LOCAL TIME 10:26 GMT www.spa.gov.sa/w