Rescue workers at the Beaconsfield goldmine in Tasmania are drilling a longer tunnel than originally planned to reach the two trapped miners.
The Australian Workers Union national secretary, Bill Shorten, says information the two men were able to give their rescuers has led to the change.
Mr Shorten says the rock is five times harder than concrete and the drilling is expected to last at least two days.
He says both men continue to help their rescuers try to reach them and a digital camera passed to them earlier had proved very useful.
"They're able to point the camera around the various parts of their fairly cramped environment, and that helps to guide the rescuers to the best spot to rescue the blokes, so the blokes are helping to rescue themselves."
Work began last night to bore a new tunnel through 12 metres of rock.
Todd Russell and Brant Webb have been trapped almost a kilometre underground since a rockfall nine days ago.