Carbon monoxide poisoning has killed seven villagers as they looked for agate stones in an abandoned mine in northeast China's Liaoning Province, local authorities said Friday.

An initial investigation shows that six people from a village in the small city of Beipiao, which is administered by Chaoyang City, entered the local mine illegally Wednesday night and died of carbon monoxide poisoning soon after, the Chaoyang municipal information office announced in a statement.

One of their friends in the village, after not hearing back from them, went down into the mine Thursday morning to look for them, but he also died of gas poisoning, the statement said.

Local police are further investigating the case.