Rescuers pulled seven injured miners to the surface Friday and were trying to reach 50 others trapped after a rock explosion in a coal mine in central China, state media reported.
Four miners were killed in the blast Thursday evening and 14 managed to escape, the official Xinhua News Agency said. The rock explosion happened just after a small earthquake shook near the mine in the city of Sanmenxia in Henan province.
State broadcaster CCTV showed rescuers in emergency gear carrying out the seven found alive Friday morning. Xinhua said six had minor injuries but one was seriously hurt.
At least 200 workers were digging a small rescue tunnel about 1,650 feet deep to try to reach the trapped miners, the People's Daily newspaper's website said. The structural status of the mine and the conditions of the miners were not known.
The Qianqiu Coal Mine belongs to Yima Coal Group, a large state-owned coal company in Henan, the State Administration of Work Safety said on its website.
Xinhua said a magnitude-2.9 earthquake occurred to the east of Sanmenxia about 30 minutes before a "rock burst."
The phenomenon occurs when settling earth bears down on mine walls and cause a sudden, catastrophic release of stored energy. The exploding chunks of coal and rock, or the shock waves alone, can be lethal.
The survival of the trapped miners depends on the intensity of the rock explosion and the rescuers' ability to provide ventilation to them, a local official told the Associated Press.
"If it was not very strong, it might have caused the tunnel to get narrower, but we might still be able to send some air in there to ensure ventilation," said the Yima city Communist Party's head of propaganda, who would give only his surname, Tian, as is common with Chinese officials.
"But if the impact was pretty strong and caused the tunnel walls to collapse, then the ventilation was probably cut off immediately, suffocating the people trapped there," Tian said.
Tian said it was difficult to determine how deep in the mine the trapped workers were.
According to Xinhua, workers were digging a tunnel about 830 yards long, but after the rock burst, the tunnel appeared to have "basically folded" a little more than halfway down the passage, at 525 yards. It was unclear what the condition of the tunnel was beyond that point, Xinhua said.
China's coal mines are the deadliest in the world, although the industry's safety record has improved in recent years as smaller, illegal mines have been closed. Annual fatalities are now about one-third of the high of nearly 7,000 in 2002.
