Rescue workers check their gear as they attempt to free Chinese miners trapped underground.

Eighteen of the 28 workers in the coal mine in southwest Guizhou Province were killed in a gas explosion Saturday.

Five miners in critical condition have been rescued.

A local official says gas levels in the mine, as well as debris blocking the tunnel, are delaying efforts to reach five more trapped miners.

China has a record of poor mine safety, with hundreds of accidents each year.

More than 1,000 miners have died this year alone despite the government's efforts to shut down small and illegal operations.