Seven people were killed in a colliery accident in Southwest China on Monday, bringing the death toll in coal mine tragedies to 85 over the past three days.

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Eleven workers who were sorting impurities from a coal heap were buried when the heap collapsed at 9:47 a.m. at the Shuicheng Coal Mine Group colliery, in mountainous Guizhou province.

Seven workers died and four were rescued, said the work safety administration in Liupanshui city, where the group is located.

The cause of the accident is being investigated.

The past weekend has been tragic with three mine disasters leaving at least 78 people dead.

Twenty-two miners were confirmed dead and five missing in Saturday's gas blast in Yuanhua Coal Mine in Jixi, a city in Northeast China's Heilongjiang Province.

Three managers responsible for the blast have been arrested, said local police. An investigation has shown at the end of August, the mine was forced by the local government to halt production due to outdated certificates of work safety, but the owners continued operations.

In another tragedy, 32 miners were killed and 28 injured in a colliery gas explosion at Changyuan Coal Mine in Fuyuan, a county in southwestern Yunnan Province.

A third gas blast on Sunday hit Luweitan Colliery in Linfen city, North China's Shanxi Province, killing all 24 miners underground, the local government said on Monday.