LONDON -- The evacuation of an American caver trapped underground in Turkey continued overnight, as a rescue team carrying him on a stretcher passed through a rest camp about 1,000 feet underground, international caving officials said.

Mark Dickey, 40, has been trapped underground since Aug. 31, when he fell ill more than 3,400 feet below the surface, according to the New Jersey Initial Response Team, a group he leads.

A team that includes medical staff began an evacuation late last week, after his condition improved enough to move him, caving officials said.

"The stretcher with Mark reached the level -300m," or about 984 feet underground, the Hungarian Cave Rescue Service said in an update posted Monday morning.

The team carrying the stretcher had passed a bivouac site about 500 meters, or 1,640 feet, below the surface about 12 hours earlier, the European Cave Rescue Association said.

"The medical status of the casualty is stable," the association had said in a statement on Sunday evening. "The next planned stop is at -300 m. The members of the different rescue teams are in a good physical condition."

Dickey's condition on Sunday was "very good," according to Tulga Sener, the medical coordinator for Turkey's Caving Federation.

"He has not had any bleeding or vomiting for at least 2 days," Sener said in a statement posted in Turkish on social media. "All vital signs, pulse, blood pressure, body temperature, state of consciousness, cooperation are all completely healthy."

When Dickey reaches the surface, he's expected to be examined at the scene by Turkish and foreign doctors, rescue officials said on Sunday. He'll then be flown via helicopter to a nearby hospital.

Dickey had been assisting in the exploration of the cave when he "suddenly became ill with intestinal problems that rapidly progressed into life-threatening bleeding and vomiting," the New Jersey Initial Response Team said in a statement announcing the his situation. Dickey serves as the leader of that group, a collection of volunteers who specialize in cave and mine rescues.

The evacuation of Dickey was expected to be hindered by narrow passages "just big enough to crawl through," the group said. Demolition teams had been working to enlarge the path so his stretcher could reach the surface.