BEIJING, June 25 (Reuters) - A fire tore through a martial arts training centre in China during the early hours of Friday morning, killing 18 people, with one state media outlet saying most of the dead were children who were staying there. The blaze broke out at 3 a.m. (1900 GMT Thursday) and was later extinguished, the government of Zhecheng county, in Henan province, said on its website. It was unclear what caused the fire, which injured 16 people, four of whom were in serious condition, it said. Most of the casualties were students aged between 7 and 16 staying on the centre"s second floor, the Beijing Youth Daily said in a report that was later deleted from its website. In a social media post, Zhonghong, a news outlet backed by China"s state planner, identified the centre as Zhenxing Martial Arts Centre. Neither Zhenxing or its founder, Chen Lin, answered calls seeking comment. "My kid is 9 years old, but I know nothing about his current situation. We can"t see him or visit him," said Zheng, the father of one of the children admitted to hospital. "At Zhenxing, the kids would study and practice martial arts in the day and live there every night. I don"t know what caused the fire," Zheng told Reuters by telephone. Another father was filled with relief that his son was among the survivors. "It"s extremely lucky that my son escaped from the fire, but I don"t know anything specific," said Xu, 39. "All information is being blocked," he said in a text-message. Police detained the person in charge of the centre, the county said. It did not identify the person or the training centre. Fires are not uncommon in China, due partly to patchy safety protocols and sub-standard construction. In one China"s most horrific fires, 309 people were killed at a nightclub in the city of Luoyang, also in Henan, on Christmas Day in 2000.