Carlos Araya stands next to Chilean flags representing the 33 miners trapped at the San Jose collapsed mine in Copiapo, Chile, Monday. (Roberto Candia/Associated Press)

Thirty-three Chilean miners trapped deep underground sang the national anthem Tuesday in a full-throated chorus, thanked their rescuers and settled in for a long wait until a tunnel wide enough to pull them out can be carved through a half-kilometre of rock.

Raising hopes further, a second bore hole was punched into the chamber where the miners are located and a third probe was nearing the site in the San Jose mine in Copiapo, about 725 kilometres north of Santiago .

After parcelling out tiny bits of food and drinking water carved from the mine floor with a backhoe for 18 days, the miners were getting glucose and rehydration tablets to restore their digestive systems.

Capsules carrying oxygen also were sent down through a 15-centimetre bore hole to help the men survive the hot, humid conditions in the lower reaches of the gold and copper mine.

Communication lines

The bore holes also will be used to lower communication lines and to provide ventilation, Mining Minister Laurence Golborne said.

The miners were sending up notes to their families in the same supply capsules on Tuesday, providing solace to people who have held vigil in the chilly Atacama desert since the Aug. 5 collapse.

However, their ordeal is far from over.

Doctors and psychologists were debating how to keep the miners sane during the estimated four months it will take to dig a tunnel large enough to get them out of the safety chamber 670 metres underground.

To prevent possible mental breakdown, doctors were debating not telling the miners about lengthy rescue efforts.

No board games to pass the time will be sent down to them because playing them could provoke competitive behaviour and hostility, experts said.

Each of the 33 miners had been living on two spoonfuls of tuna, a sip of milk, a bite of crackers and a morsel of peaches every other day.

Conserving food

They were so careful in eating what was supposed to be a two-day emergency supply that when the outside world finally reached them 17 days after a mine collapse, they still had some food left.

The miners said they have honoured the same hierarchy they used on any work shift, following the directions of shift foreman Luis Urzua, 54.

They conserved the use of their helmet lamps, their only source of light other than a handful of vehicles whose engines contaminate the air supply. They fired up a bulldozer to carve into a natural water deposit, but otherwise minimized using the vehicles that contaminate the available air.

The miners can still reach many chambers and access ramps in the lower reaches of the mine, and have used a separate area some distance from their reinforced emergency refuge as their bathroom.

But they have mostly stayed in the refuge, where they knew rescuers would try to reach them.

The room has become stiflingly hot and stuffy. Leaving it allows them to breathe better air, but wandering too far is risky in the unstable mine, which has suffered several rock collapses since the initial accident.

Rescue efforts advanced considerably Tuesday as a third bore-hole prepared to break through to the miners, and a huge machine arrived from central Chile to carve out a tunnel just wide enough for the miners to be pulled out one-by-one. That machine won't begin drilling for several days.

Andres Sougarret, the rescue effort's leader, estimated it would take three to four months to pull the men out. But Davitt McAteer, a former assistant secretary of the U.S. Mine Safety and Health Administration, called that "perhaps the most conservative model."

"Twenty-five hundred feet is not a terribly, terribly big hole to drill," McAteer said. "We ought to be able to get them out in a period of weeks, not months."