Rescuers work at the entrance to the colliery, the roof of which collapsed and trapped at least 18 people, at Ruifeng Coal Mine in Fugu County of Yulin City, northwest China's Shaanxi Province, Aug. 17, 2012. The accident occurred on Thursday evening at the coal mine when a roof collapsed in a colliery, causing at least 18 trapped underground. (Xinhua/Tao Ming)

Rescuers are on standby at the entrance to the colliery, the roof of which collapsed and trapped at least 18 people, at Ruifeng Coal Mine in Fugu County of Yulin City, northwest China's Shaanxi Province, Aug. 17, 2012. The accident occurred on Thursday evening at the coal mine when a roof collapsed in a colliery, causing at least 18 trapped underground. (Xinhua/Tao Ming)

Doctors rush to the colliery, the roof of which collapsed and trapped at least 18 people, at Ruifeng Coal Mine in Fugu County of Yulin City, northwest China's Shaanxi Province, Aug. 17, 2012. The accident occurred on Thursday evening at the coal mine when a roof collapsed in a colliery, causing at least 18 trapped underground. (Xinhua/Tao Ming)

Relatives (1st and 2nd L, front) of trapped miners wait for rescue information outside the colliery, the roof of which collapsed and trapped at least 18 people, at Ruifeng Coal Mine in Fugu County of Yulin City, northwest China's Shaanxi Province, Aug. 17, 2012. The accident occurred on Thursday evening at the coal mine when a roof collapsed in a colliery, causing at least 18 trapped underground. (Xinhua/Tao Ming)

Rescuers are on standby at the entrance to the colliery, the roof of which collapsed and trapped at least 18 people, at Ruifeng Coal Mine in Fugu County of Yulin City, northwest China's Shaanxi Province, Aug. 17, 2012. The accident occurred on Thursday evening at the coal mine when a roof collapsed in a colliery, causing at least 18 trapped underground. (Xinhua/Tao Ming)