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The death toll has climbed to 20 after two carriages carrying mine workers back to the ground crashed early Tuesday in a pit of Northwest China's Gansu province.

BEIJING - Thirteen miners were confirmed dead and seven remained trapped after a locomotive that transported them to ground slipped down a pit in Northwest China's Gansu province early Tuesday morning, the provincial administration of work safety said.

The locomotive with 34 workers aboard its two carriages slipped down and overturned 150 meters further at 0:25 am when a steel wire powering the vehicle up a 28-degree 704-meter-long slope broke 80 meters away from the entrance of a colliery pit in the city of Baiyin, the agency said in a new update.

A total of 27 workers at the Qusheng Coal Mining Co have been taken out of the pit, but 13 of them were dead, it said.

The rescue operation is still under way.

The coal mine, which began operation in 2003, has a designed annual production capacity of 90,000 tonnes.