Officials of the coal mine were detained, while authorities are investigating its business operations

The death toll from a gas explosion in a Chongqing coal mine rose to 18 on Tuesday, as rescuers worked around the clock to search for the 15 miners who remained trapped more than 24 hours after the blast.

Rescuers found the bodies of another five miners in the coal mine on Tuesday after the bodies of 13 miners were discovered in a pit 93 meters below ground on Monday night.

Of the 18 bodies, 17 have been removed, with rescuers still trying to remove the other as of Tuesday evening. The gas explosion took place at the Jinshangou coal mine of Yongchuan district at 11:33 am on Monday.

The rescue headquarters said at a news briefing on Tuesday evening that the density of gas in some areas within the coal mine remained high, and they are pumping out the gas as the search and rescue efforts continue.

Meanwhile, the fact that there are collapsed tunnels within the coal mine has made the use of large machinery impossible, forcing rescuers to clear the debris in the tunnels manually and to fortify the tunnels first before reaching the trapped miners, the authority said.

There were 35 miners working when the incident occurred, and two workers were able to escape unharmed, it added.

More than 400 rescuers have been working overnight, taking turns going down the shaft for the search and rescue operation, according to the headquarters.

Yang Huanning, minister of the State Administration of Work Safety, said at the scene that the investigation should be conducted along with rescue efforts.

"(The rescuers) should pay special attention to the gathering, recording and saving of important evidence," he said.

He also stressed the importance of avoiding secondary disasters and cracking down on illegal behaviors that violate work safety regulations.

Gui Laibao, deputy head of the State Administration of Coal Mine Safety, told Xinhua News Agency that a preliminary investigation has found a problem with mining beyond the legal boundaries.

He added that there were problems with work safety facilities and improper ventilation systems.

Luo Qingquan, head of Yongchuan district, told Xinhua News Agency that police have detained the legal representative and manager of the coal mine, and authorities are investigating its business operations, including the payment of workers and whether miners have life insurance.

Mu Huaping, vice-mayor of Chongqing, said at a news conference on Tuesday evening that "the tragedy is a big lesson for us", adding that the mine had serious issues with safety management and that related departments will be punished.

The municipal authority will close all mines with a yearly production volume of less than 90,000 metric tons before the end of this year, he said.

The privately owned Jinshangou mine has a designed annual output of 60,000 tons, according to its license. The coal mine has 150 workers.

Contact the writers at tanyingzi@chinadaily.com.cn and xuwei@chinadaily.com.cm