A gas explosion inside a tunnel at a construction site in Sichuan province killed two people, left two missing and injured a further 53, Xinhua reported yesterday. The blast on Tuesday at a reservoir project, located at the border of Wenchuan county and Dujiangyan , was apparently triggered by underground gas, the report said. Dujiangyan is famous for its flood control and irrigation scheme, built 2,250 years ago. 'I've seen gas burning on the tunnel ceiling three times but I did not report it to supervisors because I believed it was normal to have gas burning in tunnels,' Xinhua quoted Li Huaxu , a 17 year old who works at the site, as saying. The youth said he had been heading to the work shed less than 100 metres from the tunnel at the time of the blast. 'I heard a loud explosion and saw smoke and dust from the tunnel. My father was inside, so I rushed into the tunnel for him and helped him and other injured out,' he was quoted as saying. About 28 of the injured workers were seriously hurt. Ten who were in a critical condition have been sent to hospitals in the provincial capital, Chengdu , Xinhua said. The 918-metre-long tunnel was in an area due to be submerged once the reservoir, one of 10 big development projects for the region, was completed, the report said. In May, five people were injured in a blast in the same tunnel. Construction workers told local newspapers that sections of the tunnel had collapsed earlier on Tuesday, but the construction workers were still sent into the tunnel to work. A project supervisor told the West China Metropolis News that he had sent safety experts into the tunnel after the collapses to check for gas leaks.