Six people were found dead after a mudslide buried workers at an illegal gold mining site in Indonesia’s Central Kalimantan province, an official said on Friday.

Two other miners survived the accident in Kutawaringin Timur district on Thursday, said Rihel Magat, the head of the local civil protection agency.

“We suspect that water sprayed by the workers who were digging the mine caused the shaft to collapse.

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“It was a case of poor mining technique,” he said.

Deadly accidents are common in artisanal mining sites in Indonesia.