Investigation ordered after recovery of the bodies by rescuers at Jinshangou mine where the blast occurred on Monday.

All 33 coal miners trapped underground in a gas explosion earlier this week in China’s Chongqing region have been found dead, according to Chinese state media.

Two miners survived Monday’s explosion but rescuers working around the clock found no others alive at the privately owned Jinshangou mine, where the explosion occurred before midday.

All the bodies have been recovered and rescuers were shown bowing their heads in memorial for the dead.

Gas explosions inside mines are often caused when a flame or electrical spark ignites gas leaking from the coal seam.

Ventilation systems are supposed to prevent gas from becoming trapped.

The State Administration of Work Safety ordered an investigation, saying thta those responsible must be strictly punished.

Local officials in Chongqing also ordered smaller mines to shut down temporarily.

China’s mining industry has long been among the world’s deadliest.

The head of China’s State Administration of Work Safety said earlier this year that struggling coal mines are likely to overlook maintenance.

China is the world’s largest producer and consumer of coal but has announced plans to shut more than 1,000 outdated mines, as part of a broader plan to cut down on overproduction.