XI'AN, Jan. 6 (Xinhua) -- Eleven people were trapped underground following a coal mine cave-in in northwest China's Shaanxi Province Wednesday, local authorities said.

The collapse occurred in a pit of Liujiamao Coal Mine at Shenmu County of Yulin City, at around 9 a.m. Wednesday. At the time of the accident, 49 miners were working underground and 38 of them succeeded in fleeing for life, the county government said.

The rescue work is hampered by the high density of poisonous gas underground and rescuers are mainly restoring the ventilation system.

The rescue staff have entered the shaft three times, but still were more than 1,000 meters away from the trapped site.

The mine owner has been held by police.

An investigation into the cause of the cave-in is under way.

The privately-owned Liujiamao Coal Mine is operated on test run, rescuers said.