Rescuers have dug 300 meters into the main shaft of a coal mine in south China's Guangxi Zhuang Autonomous Region, where a cave-in trapped 19 workers and killed three on Saturday.

But high levels of explosive gas and siltage in the shaft hindered rescue efforts, making it difficult for the rescuers to reach the trapped miners, who were located at 390 meters underground, said Zheng Zhao'an, head of the emergency rescue headquarters in the suburbs of Heshan City.

Zheng said rescuers were digging a second rescue channel in an adjacent shaft, hoping to provide a backup route for the rescue.

The cave-in happened at midday Saturday. Investigators said it was caused by continuous downpour.

Heavy rain forced mine authorities to halt production for three days from June 29 to July 1. Operation was resumed on Saturday.

Altogether 71 miners were working in the pit when the accident happened. Forty-nine managed to escape.