A California teen’s arm was partly severed after he spent nearly an hour trapped under a “cooler-size” boulder that fell on top of him, reports said.

Emergency responders descended on the Emerald Bay area of Laguna Beach shortly before 3:30 p.m. Wednesday to rescue the 15-year-old boy, who had been walking on a rocky cliff with a friend when the accident happened, KABC-TV reported.

The harrowing ordeal lasted about 40 minutes, until personnel from the Laguna Beach Fire Department used heavy-duty airbags to hoist the rock off the teen’s leg and arm, which was partially amputated by the boulder, the outlet reported.

He was airlifted to the trauma center at UC Irvine Medical Center in serious condition, the outlet said.

Tanya Leah Lugo was climbing in the same spot as the teen just moments before the boulder tumbled down and crushed his limbs.

“I assumed that he was dead because everything got real silent and somber. But then you saw the helicopter,” Lugo told KABC.

“I saw his mom, and she was crying. She was looking very panic-stricken.”

Orange County Fire Authority Capt. Tony Bommarito, who admitted an accident like this hasn’t been seen in nearly three decades, nonetheless warned hikers that the cliffs aren’t monitored and that walking on the side of one is always a risk.

“You have to assume there’s some risk because we don’t know if that cliff is stable or not,” Bommarito told KABC.

“It’s an unfortunate accident … Wrong place at the wrong time, so just a very sad situation.”

Lugo said there are no signs warning of falling rocks, but authorities told the outlet that boulders “constantly fall.”