Three young students from Sydney travelled to Gerringong Falls, in the Budderoo National Park on Jamberoo Mountain, on Sunday afternoon.

Andrew McCullough, a spokesperson for the State Emergency Service, said two of the students began to abseil over the edge around 1pm while the third stayed at the top.

The two abseilers soon hit difficulty, however, as they had only packed an 80 metre rope for a 160 metre descent.

"They were unprepared. They only had a short rope, and got stranded about halfway down," Mr McCullough said.

"It is a 160-metre cliff face with a waterfall, one of the highest cliffs in the area."

The third student climbed down the cliff face in an attempt to help his friends, but could not get them free. He climbed back to the top of the cliff and contacted emergency services around 6pm - five hours after the trio started their adventure.

SES, police rescue and ambulance crews rushed to the scene, arriving at about 6.30pm.

Mr McCullough said they were assisted by an employee of the National Parks and Wildlife service, who helped rescuers find and follow bush tracks to the cliff.

"It would have been much harder without him and his local knowledge," Mr McCullough said.

SES and police rescue crews set up hauling systems at the top of the cliff, as an SES rescue operator abseiled down to find the two students on a cliff ledge.

Using the harnesses they were already wearing, the students were lowered down the cliff and met by emergency services crews.

The trio emerged from the area after 11pm - 10 hours after they first went over the edge.

Mr McCullough said the incident could have been worse, and said it highlighted the need for proper preparation in such activities.

"Coming into summer time, people head outdoors but you need to make sure you're prepared," he said.

"These activities need proper experience and equipment, and you should always carry a satellite beacon."