The Chilean government says rescuers hope to reach 33 miners trapped underground by Sunday.
Mining Minister Laurence Golborne said drilling equipment was being changed in preparation for the final push, but it would be three to eight days before the rescue mission would begin.
Engineers said on Saturday the shaft was now just 34 metres from the chamber, the BBC reports.
The miners were trapped 700 metres underground when part of the San Jose mine collapsed on 5 August and have now been underground longer than any other group.
Andre Sougarret, the engineer in charge of the drilling, said the final part of the operation would have to be handled very carefully.
"There are dangers - that we break through the hard rock, and when we break that, someone might get injured."
Mr Golborne said a camera sent down the shaft would help determine if the miners could be winched up through the exposed rock, or if they would have to wait for the shaft to be encased with steel piping.
Huge cranes have been brought in to lower the metal casing if it is needed.
Officials say everything needed for the rescue is in place and it expected to take an hour to winch each man to safety.