The 17-year-old suffered a broken arm and an injured pelvis in the fall, which sparked a dramatic rescue by more than 20 emergency services personnel who battled fading light and steep terrain to carry him out.

Friends called triple-0 after the boy toppled over the top of the falls and disappeared from sight about 6pm.They said he hit rocks multiple times as he fell before landing in the water.

A Snowy Hydro SouthCare helicopter was called to the isolated area, which is off limits to members of the public, to winch the boy to safety.

ACT Fire and Rescue crews were called after the helicopter had to abandon the rescue because of technical problems.

Paramedics treated the boy on rocks next to the water before floating him in a stretcher to the other side of the falls where he had to be lifted up a four-metre rock face using a harness.

It then took more than two hours for crews to carry the stretcher 400 metres up a rocky incline before they emerged and transferred him to an ambulance shortly after 9pm.

ACT Fire and Rescue commander Michael Cochrane said a group of vertical rescue experts used high angle rescue techniques and rope work to move the teenager, who was conscious the whole time.

"He's going pretty well, he had a couple of paramedics who were with him the whole time and were able to administer some pain relief.

"Just as well he had friends here who were able to call for help."

The boy's family and friends who gathered near the top of the falls said they were too upset to comment, but one man said the group wanted to thank emergency crews for their efforts.

Mr Cochrane said the incident was a warning for ACT residents who flocked to water holes throughout summer.

"Wet rocks are slippery and don't walk across them," he said. "Also, I believe this area has been closed to the public for some time."