A coal mine gas leak in southwest China has killed at least 29 miners and six others were missing, the state-run Xinhua news agency reported Friday.

The report said 86 miners were working in the shaft in the Qunli Coal Mine in Guizhou Province when gas began to leak Thursday afternoon, trapping 34 of the miners -- 28 of whom died. The rest were rescued but one died after treatment, raising the death toll to 29.

The bodies of the 28 trapped miners were recovered from underground.

"The other six miners have slim chances of survival, but search will continue," a rescuer said.

The cause of the gas leak has not yet been determined.

The Xinhua report said Qunli Coal Mine is a licensed colliery with an annual production capacity of 300,000 tons. Accidents in Chinese mines kill an estimated 10,000 people each year, state officials said.