A leak of toxic gas killed two and sickened another six at a ferronickel mine in northwest China's Qinghai Province early Saturday, the local safety authority said.

A Cyanogen sulfide leak was detected at around 1 a.m. at Yuanshishan ferronickel mine in Ping'an county of Haidong City, Qinghai provincial safety administration said in a press release.

It said rescue began immediately after the accident, and the sickened miners were rushed to hospital.

The cause of the leak is still under investigation, the document said.

Cyanogen gas is colorless with a pungent odor. Inhalation can lead to headache, nausea, loss of consciousness, convulsions and death.