LIAOYANG, Liaoning - A senior state work safety official on Monday blamed the cover-up of a Liaoning province coal mine accident and the flight of the mine boss for missing "the best time" to save 17 miners trapped underground after the incident.

Work crews on Monday were still pumping out poisonous gas that prevented rescuers from entering the Dahuang No 2 Coal Mine in the city of Liaoyang, where a gas explosion last Thursday killed at least five miners and trapped 17 others.

Fu Jianhua, deputy director of the State Administration of Work Safety, who is supervising the rescue and investigation at the scene, said an initial probe shows the mine illegally re-opened after being ordered to shut for a safety overhaul.

"The mine failed to meet the safety requirements for operation," Fu said. "And the accident was initially covered up while the mine owner fled, resulting in a delay in the rescue."

Police earlier said they have detained the mine owner and another three managers.

Fu vowed to thoroughly investigate the case and severely punish the people found responsible.

He also ordered enhanced efforts to ventilate the carbon monoxide and other poisonous gas in the pit. Engineers said the mine's ventilation barely worked, pumping out only 80 cubic meters of gas per minute, far below the 1,000-cubic-meters-per-minute national standard for safe mining.

China's mines are among the deadliest in the world. Fatal accidents frequently occur in unlicensed mines eying huge profits in the sector. The State Administration of Work Safety reported that 1,973 miners were killed in coal mine accidents last year. The death toll, however, was 19 percent lower than the figure recorded in 2010.