A group of spelunkers on Sunday was about 400 feet deep in an upstate New York cave when one of them, a Brooklyn man who was belly-crawling through a precarious stretch known as the bear trap, plunged into a crevice and was pinned for six hours, the authorities said.

Three friends tried to free him by chipping away at the rock with a hammer. But that didn’t work, and after a few hours, they all began to develop hypothermia, said Lt. John Gullen, a forest ranger with the New York State Department of Environmental Conservation, who led the rescue mission.

It took rescuers, including members of the Albany-Schoharie Cave Rescue Team, another three hours and a rock drill to free the man from the passageway, which is part of Merlins Cave in Canaan, N.Y., about 30 miles southeast of Albany.

The man was treated for hypothermia but was otherwise unharmed.

“I was able to squeeze my way over top of the subject and then get behind him by his feet,” Lieutenant Gullen said in an interview with CBS6 Albany, adding that the man “was really jammed in there.”

“His full body was stuck in a crevice that was basically designed the exact shape of him,” the lieutenant said.

The explorers were leaving the cave when the man became wedged around 6 p.m., said Greg Moore, a co-captain of the Albany-Schoharie Cave Rescue Team.

All of the spelunkers were experienced cavers and had permission to be there, Captain Moore said.

After other members of the party tried to rescue the man on their own, a few left the cave to call 911.

The mouth of the cave is atop a mountain roughly a mile from the road through woods. Firefighters had to bring two off-road vehicles to transport rescuers back and forth to reach the cave.

Captain Moore said there were about a dozen firefighters, two medical doctors, eight rescuers and six spelunkers on the scene by the time he arrived.

He said that the rescuers had brought miniature Reese’s Peanut Butter Cups for the trapped man, to keep his energy up.

“We first tried some ropes and webbing — rock-climbing equipment — to try pulling him up,” said Emily Davis, the other co-captain of the rescue team. “But we couldn’t.”

Next, rescuers tried drilling.

After nearly two hours, Lieutenant Gullen was able to pull the man a few inches out of the fissure. The Department of Environmental Conservation did not publicly identify the rescued man.

“He was really jammed in by this one nub of rock,” Lieutenant Gullen said in the CBS6 interview, adding that he had used a special tool to drill into the rock just inches from the man’s head.

Captain Moore, who is also the Northeastern regional coordinator with the National Cave Rescue Commission, described it as “a heavy-duty battery-powered drill,” adding that it was “nothing super fancy.”

Caves in New York State remain around 50 degrees year round and are extremely humid. The rock walls are damp and cold.

“Laying on the rock, he’s getting a bunch of heat sucked out of him,” said Kyle Gochenour, a Tennessee-based cave rescuer who trains others through the National Cave Rescue Commission. “Caves run so cold. Losing heat becomes the bigger risk.”

Cave rescues are rare.

Hazel Barton, a cave explorer and geology professor at the University of Alabama, said that trained cavers get stuck once every 50,000 trips or so, usually because of something spontaneous, like a rock fall.

Captain Moore said, “If we get a rescue or two in a year, that’s a busy year for us.”

Merlins Cave is on a 35-acre preserve, next to another cave called Dragon Bones.

Both are closed to explorers from October through April to protect hibernating bats, according to Erik Nieman of the Northeastern Cave Conservancy, which owns the caves.

“The group that was with the trapped gentleman was really good,” Captain Davis said. “They did everything right.”