Doctors are still trying to assess the long term effect of injuries sustained by one of two boys injured on Monday when they came off their bikes in the Jervis Bay area

Two bikes collided late Monday afternoon in the St Georges Ave Reserve near Erowal Bay

One of the riders, a 12 year old, suffered possible spinal injuries,  a major fracture to his upper leg, and shoulder lacerations.

He was flown to  hospital in the ambulance rescue helicopter., which landed at the sporting fields near the Bay and Basin Leisure Centre.

Doctors are still conducting tests to confirm the extent of the boy's injuries

The second boy also suffered multiple, but less serious injuries, and was taken by road ambulance to Shoalhaven Hospital.

Police inquiries into the crash are continuing.