A coal mine in central China's Henan Province where an underground explosion killed 47 people Monday was operating illegally, officials said Tuesday.

The operation license of Xingdong No. 2 Mine in Weidong District, Pingdingshan City, expired on June 6, and the district government cut its electricity supply on June 7, according to local officials.

But mine manager Liu Jianguo still managed to produce coal even as 10 district government supervisors were stationed at the mine, said Luo Lin, head of the State Administration of Work Safety.

The shaft should have been sealed with concrete, but instead it was covered with a moveable cement board, reporters at the scene saw.

"The accident shows safety regulations were not strictly observed at the grassroots level and that some regulators may be in cahoots with mine owners," said Luo.

Seventy-five miners were underground when the blast occurred. Twenty-five of the 28 rescued miners were taken to hospital and one has been discharged. Fifteen are stable and the other nine are in serious condition.

The State Council established an investigation team Tuesday, led by Luo Lin, head of the State Administration of Work Safety, and comprising members from the State Administration of Work Safety, the State Administration of Coal Mine Safety, the Ministry of Supervision, the All-China Federation of Trade Unions, the Ministry of Public Security and Henan Provincial Department of Supervision.

Poisonous gas entered the underground workplace after the blast, which was caused by illegally-purchased explosives, Luo Lin said.

Further investigations would be launched into the source of the explosives, the specific production processes, malpractice and possible corruption of the officials, said Zhao Tiechui, a deputy director of the work safety and coal mine safety administrations.

A number of local officials were removed from their posts Tuesday.