The 52-year-old woman was injured while walking the Jatbula Trail near Katherine in the Northern Territory with a group.

The 62km trail follows the Arnhem Land escarpment along the edge of Nitmiluk Gorge to Leliyn Falls.

The trek normally takes five to six days.

The group was three days into the well-known walk when, while crossing a rocky path near Crystal Falls, a large boulder was dislodged and rolled onto the woman, trapping her by the leg.

Emergency help was called and a doctor walking with the group provided initial care for the woman.

It's understood St John ambulance paramedics and rangers arrived on scene first with the use of a helicopter.

SES and NT Emergency Service crews arrived later by road.

CareFlight, operating the Top End Medical Retrieval Service on behalf of the NT Government, tasked the NT Rescue Helicopter with flight doctor and flight nurse aboard.

As the CareFlight team arrived, the SES crews had begun using hydraulic equipment to extricate the woman from beneath the boulder, which was estimated to weigh several hundred kilos.

CareFlight's doctor and nurse provided treatment for the woman for suspected leg fractures and exposure while she remained trapped and throughout her extrication.

The woman was freed by about 10pm after being trapped from around 5.30pm.

The emergency service crews and bystanders joined CareFlight's medical team to carry the woman in a stretcher across a creek and over the steep rocky ground about 150 metres to the helicopter.

The woman was escorted by her son as she was airlifted to Royal Darwin Hospital in a stable condition.

CareFlight's team would like to thank all the emergency service staff, rangers and bystander involved for their help.

Katherine Times