Updated

A teenager who sneaked onto an oil well site to play on the equipment got tangled in a piece of machinery and a doctor had to amputate his left arm to free him, firefighters said.

The 17-year-old boy and his friend jumped an 8-foot fence Sunday to play with a pump jack, a common piece of oil field equipment that rocks up and down to lift oil out of a well.

He turned on the machine to ride it but became entangled in one of its moving parts, and his friend couldn't shut it off, Fire Chief Cecil Clay said.

The friend flagged down a taxi driver, who turned it off. But firefighters were unable to free the boy without further endangering him, so a surgeon was flown in on a medical helicopter to perform the emergency amputation.

The boy, whose name was not released, was then airlifted to the University of Oklahoma Medical Center.

Hospital spokesman Allen Poston said the family requested that no information be released.

"I would caution anyone who's heard stories about riding these pump jacks and getting out here and messing with them to write that off," Clay said.

"It's not that much fun anyway. It's dangerous."