Rescuers were searching for 166 workers who were trapped in a coal mine in northern China yesterday after a massive explosion tore through the shaft in what could be the country's worst mining accident in recent years.

　　Another 127 miners, many of whom were working near the entrance of the state-owned Chenjiashan Coal Mine in Shaanxi Province, managed to escape after the early morning blast, Xinhua news agency said.

　　The accident came just weeks after another explosion in central Henan Province killed 148 workers - the highest death toll since 2000. It was triggered after mine operators failed to realize that extending the mine's shaft would greatly increase its gas level.

　　In Shaanxi, 41 workers were hospitalized yesterday, five with serious injuries, Xinhua said. Many were suffering from carbon monoxide poisoning, it said.

　　Witnesses said they saw "huge amounts of thick smoke pouring from the mine's ventilation vents," hampering rescue efforts, according to the Website of People's Daily newspaper.

　　President Hu Jintao urged rescuers to employ "all effective measures" to save the trapped workers, according to state television.

　　Premier Wen Jiabao, who arrived at a summit of the Association of Southeast Asian Nations in Laos yesterday, said he was "extremely upset" over the accident.

　　He said the cause of the explosion would be thoroughly investigated and that the government will continue to push for safer working conditions in the mines.

　　Main provincial Party and government leaders, including Li Jianguo, secretary of the Shaanxi Provincial Committee of the Communist Party of China, and Chen Deming, acting governor of Shaanxi, rushed to the site of the accident to organize the rescue operation, Xinhua said.

　　State television showed ambulances speeding to the scene along a dusty dirt road as huge crowds of people gathered outside the main gate of the mine.

　　Xinhua said the explosion occurred when 293 workers were underground and was centered around coal pits 8 kilometers from the mine entrance.

　　Staff at Chenjiashan lost communications with the missing miners early in the day, the People's Daily said.

　　According to Xinhua, Chenjiashan is a state-owned venture capable of producing 1.3 million tons of coal a year.

　　China's mines are the world's most dangerous, with thousands of deaths reported every year due to explosions, fires, cave-ins and flooding often blamed on lax safety rules and lack of required equipment.

　　The government has vowed to improve conditions and frequently orders mass shutdowns and safety checks after a fatal mine accident.

　　But despite the crackdown, accidents still happen on a near daily basis.

　　Also yesterday, 16 officials in the northern Hebei Province were charged with helping to cover up a coal mine explosion on June 3 that killed 14 miners and injured 23 others, Xinhua said.(The Associated Press)