XI'AN -- Eleven people were killed in a gas blast at a coal mine in Northwest China's Shaanxi province, local authorities said.

Altogether 21 miners were working underground when the blast happened at 11:38 am at the Tianyu Coal Mine in Zhaojin Township of Yaozhou District in Tongchuan city, a spokesman with the city government said.

Ten miners were lifted above ground safely after the blast, and two of them suffered minor injuries, the spokesman said.

The bodies of the 11 miners killed in the blast had been retrieved, he said.

The coal mine reports an annual output capacity of 150,000 tonnes.

Local authorities are investigating the cause of the blast, the spokesman said.