SANTIAGO - Workers will begin drilling a rescue shaft for 33 miners trapped deep underground in northern Chile early Monday, the engineer in charge of the rescue operation said.

"The drilling machine is being installed... we expect to start working with it on Monday morning," Andre Sougarret told AFP.

"The shaft we're drilling to the shelter will go down 702 meters (2,303 feet) in a straight line," he added, referring to the hot and damp space where the men have been huddled for over three weeks.

He said the drilling operation was expected to last three to four months, in line with previous estimates.

The rescue shaft will be 66 centimeters (26 inches) wide -- the same as a bicycle wheel -- allowing the miners to be pulled one at a time.

The miners have been trapped since an August 5 cave-in at the San Jose gold and copper mine near Copiapo, 800 kilometers (500 miles) north of Santiago.