BEIJING, Nov. 2 -- A preliminary investigation has unearthed evidence indicating that a fatal gas explosion at a coal mine in the southwestern municipality of Chongqing on Monday was due to operational negligence.

It is alleged that Jinshangou Coal Mine had operated beyond its mining boundaries; used outdated, insufficient or malfunctioning equipment; failed to ensure adequate ventilation; and its health and safety management was deemed "disorderly," the office of the State Council's work safety committee said in a statement released Wednesday.

All 33 miners who were trapped underground by the explosion have been found and pronounced dead, according to the investigation team.

Safety officials vowed to "seriously punish" those responsible for the incident.

The State Council called for a nationwide health and safety review, and that small mines, like the one in Chongqing, be closed immediately.

Altogether 35 workers were underground at the time of the incident, which happened just after 11:30 a.m. Monday. Two escaped unharmed from the coal mine in Yongchuan District.

Jinshangou mine has a designated annual output of 60,000 tonnes, according to its license.