It said the mine workers were thought to be at a depth of about 450 metres, adding that it was possible they had managed to reach an underground shelter, which contains three days worth of food, water and oxygen.

Camila Merino, Chile's labour minister, joined rescue workers and relatives of the miners at the scene of the collapse on Friday.

She said due to the blockages caused by the collapse, rescue workers were trying to access the mine through ventilation shafts.

"We must work very carefully because if we create a new collapse it will put rescuers at risk and harm the ability to get people out quickly", she said.

'History of accidents'

Major mining accidents are not frequent in Chile because of tight government controls.

Compania Minera San Esteban Primera, the mine owner, said it was unclear what caused the collapse, but insisted that all necessary precautions had been taken.

Felix Medina, a local union representative, however, told the Reuters news agency that the San Esteban mine had a history of accidents, with at least 13 deaths on site recently.

"This is an area with a lot of mining activity but the authorities don't have the resources for proper supervision," he said.