A botched robbery at a coal mine in Dianwan township, Shanxi province, northern China, resulted in ten people dying from suffocation, China's State Administration of Work Safety said.
On 26 October 14 people broke into the shuttered mine, two of which escaped through the underground tunnels on 27 October.
Two other workers were rescued and ten bodies found on 28 October.
The safety watchdog said the alleged thieves dug a tunnel to get inside the shaft and were trying to steal equipment, cables and metal railings.
Police have detained the survivors.
It was not yet known if the victims had become lost or been trapped underground by a cave-in.
A Dianwan township police officer said an investigation was taking place at the location though it was believe the victims were most likely suffocated or poisoned by noxious gas.
The State Administration of Work Safety said in October 2008 local officials had ordered the mine to be shut down and the main entryway was blasted to prevent people from entering.
The watchdog did not reveal the reason behind the closure of the mine but the government has been shutting down thousands of small, poorly managed mines in a bid to reduce the sector's high death toll.
China's mines are considered the world's most dangerous, with six miners killed every day in the first half of 2009.
Most deaths are attributed to safety failures, including a lack of ventilation or fire control equipment.