The death toll from a gas explosion at a Chinese coal mine has climbed to 87, with rescuers still searching for 21 miners.

Officials with the local coal mine safety bureau said Friday that gas density in the mine is so high it makes rescue efforts dangerous.

The latest explosion happened Wednesday at the Liuguantun mine near Tangshan city in Hebei province. Only 30 miners are known to have survived the blast.

China's mines are the deadliest in the world. Thousands of miners are killed each year.

On Tuesday, rescuers recovered the body of the last miner missing in a November 27 coal dust explosion in Heilongjiang province, bringing the number of deaths in that blast to 171.

Some information for this report provided by AP, AFP and Reuters.