Rescuers said Monday night that the high density of gas has hampered rescue efforts after 12 miners were trapped in a flooded coal mine in southwest China's Guizhou Province Sunday morning.

Four pumps are working round the clock to pump water out at the Fuhong Coal Mine located in the provincial capital Guiyang, but the risk of gas explosions has slowed rescue progress, Pu Jianjiang, chief of the provincial work safety supervisory management bureau said at the rescue site.

Rescuers were knocking above the water line in the shaft Monday, but did not hear any response from inside, possibly due to the large amount of noise at the scene, said Pu.

Life signs were identified Sunday, but it was not clear how many miners remained alive, he added.

Rescuers are rushing to pump water out and dig a tunnel to deliver food, water and oxygen.

The accident occurred at about 9 a.m. Sunday in Jinyang New District of Guiyang City, trapping 12 miners.

The investigation of the cause of the accident is still under way.