Chilean rescue workers are drilling into the last 100m of rock to reach miners trapped a half-mile underground and may begin pulling them out by the end of the weekend, it has been revealed.

One of the three rescue shafts reached a depth of 520m on 6 October, about 100m short of where the miners took refuge after the collapse of San Jose copper and gold mine on 5 August.

After the drilling rig reaches the trapped miners on 8 October, a video camera will be sent down to determine if the shaft is stable enough to pull out the workers without first casing the walls.

However, installing a steel casing would take three or four days and rescue operations could be delayed.

Chile’s state mining company and BHP Billiton are working on drilling rescue shafts.