Lachlan Rogers from Kiama was spearfishing with friends at Storm Bay when he was hit by a spear, just above the ankle.

Kiama Jet Rescue Boat captain Rhys Dawson said a member of the public reported the incident to Kiama Surf Life Saving Club volunteers, who were carrying out maintenance in a nearby shed. 

Lifesavers then took the surf rescue boat out to Storm Bay to rescue the 12-year-old from a rocky outcrop and brought him back to Kiama Harbour where paramedics treated him, just after 2pm.

Kiama Municipal Council lifeguards were also in attendance.

NSW Ambulance Inspector Geoff Senior said paramedics responded to reports a young male was caught on an island with a spear in his leg.

Inspector Senior said he talked the boy and his friends through the ordeal from the rocks during the rescue and a doctor from the NSW Ambulance helicopter was due to remove the barbs.

He expected the boy would be taken to Shellharbour Hospital once he could be transported.

"He's not in trouble, it was only superficial," he said.

Lachlan is grandson to retired Kiama surf lifesaver Murray McMillan, who was also at the scene.

"His mates were good, they stuck with him," he said.

"He's a pretty strong lad."