Ten people are trapped underground after a coal mine that was under construction collapsed Tuesday in northwest China's Xinjiang Uygur Autonomous Region.

Altogether 21 workers were in the shaft when the accident happened at about 10 a.m. Tuesday at the Shajihai Coal Mine in the Mongolian Autonomous County of Hoboksar, and 11 were lifted safely to the ground, a county government spokesman said.

Local authorities have launched a rescue operation, he said.

The cause of the collapse is being investigated, he said.

More than 110 people have been dispatched to rescue the trapped, but their efforts have been hampered by various difficulties, a spokesman with the Xinjiang coal mine work safety bureau said late Tuesday.

"The collapse site is as deep as 700 meters underground, and the collapsed part is estimated to be 500 to 600 cubic meters. The geological structure underground in very loose. In addition, water has begun gushing in the shaft," he said.

"We have not established contact with the trapped workers so far, and we have no idea about their situation," he added.

The Shajihai Coal Mine, owned by the Luneng Coal-Electricity Development Co. Ltd., is designed with an annual output capacity of 900,000 tonnes. Construction started in June last year and it is expected to be in operation in October next year.