Three men have been flown to Royal Darwin Hospital after their helicopter crashed during an animal control muster in the southern part of Kakadu National Park earlier today.

Two people were trapped in the crashed helicopter, while one was able to free himself and call for help.

CareFlight, operating the Top End Medical Retrieval Service on behalf of the Northern Territory Government, sent the NT Helicopter and a King Air to the area.

The NT Helicopter hovered above the accident scene and winched a Flight Nurse and Doctor down to assess and provide initial treatment for the patients.

The first patient was freed and winched into the helicopter before being flown to meet a CareFlight King Air at Cooinda Lodge for transport to Royal Darwin Hospital.

A CareFlight Flight Nurse and Doctor continued to care for the 59-year-old man during the transfer to RDH.

He arrived in a serious condition with significant injuries, and will be transferred to Alfred Hospital in Victoria onboard a CareFlight Jet for further treatment.

The other two patients were treated at the scene, before being winched into the helicopter and flown directly to Royal Darwin Hospital and arrived just after 6pm.

Both patients, in their 50s, were in a serious condition.

CareFlight would like to thank NT police and emergency services, RAAF, Jabiru Airport staff, clinic staff, park staff and bystanders who all assisted with this complex mission.