At least 15 people have been killed and 15 others severely injured after an explosion ripped through a gas plant in China's Henan province, authorities said on Saturday.A device in the gas factory owned by the Henan Coal Gas (Group) Co. Ltd., located in the city of Yima, exploded on Friday evening, according to the government of Sanmenxia City, which administers Yima.The injured were sent to hospital for treatment. Rescuers were searching for the missing people, authorities were cited as saying by Xinhua news agency.The Ministry of Emergency Management sent a work team, while the National Health Commission dispatched medical experts to the site.Further investigation into the incident was underway.