Rescue teams began the arduous process Saturday of extricating an American researcher who became seriously ill while he was 1,000 meters (3,000 feet) below the entrance of a cave in Turkey, an official from Turkey’s disaster management agency said.

It could take days to bring Mark Dickey to the surface since rescuers anticipate he will have to stop and rest frequently at camps set up along the way as they pull his stretcher through the narrow passages.

“This afternoon, the operation to move him from his camp at 1040 meters to the camp at 700 meters began,” the official from the Disaster and Emergency Management Directorate told The Associated Press.

The 40-year-old experienced caver began vomiting because of stomach bleeding while on an expedition with a handful of others in the Morca cave in southern Turkey’s Taurus Mountains.

Teams of rescuers from across Europe have rushed to Dickey’s aid. A Hungarian doctor reached and treated him inside the cave on Sept. 3. Doctors and rescuers have since been taking turns caring for him.