Emergency services were called to Townsville Airport about 7pm on Wednesday and put on standby on the runway as the military transport plane's crew tried to fix the problematic front wheels.

"Defence can confirm a RAAF C-130J Hercules transport aircraft made an unplanned precautionary landing at RAAF Base Townsville on 17 October 2018," a Department of Defence statement said.

"The crew were alerted to a hydraulic issue with the aircraft and acted in accordance with their response plan.

"The crew carried out procedures for the manual extension of landing gear and wing flaps, and landed safely at RAAF Base Townsville at approximately 7pm.

"Defence can confirm that the nose landing gear was extended for the landing.

"RAAF technicians are investigating and repairing the fault, and a safety investigation will be completed into the circumstances.

"Defence has ruled out this fault affecting other aircraft in the fleet and ongoing operations are unaffected."

Christine James, who claimed to have witnessed the incident, wrote on Facebook: "I just watched it circling for well over 30 minutes. Then saw another aircraft fly under it probably checking the landing gear. Saw it coming in for landing after all that time."

The Department of Defence would not say how long the aircraft spent above Townsville Airport rectifying the fault or whether another aircraft flew underneath to inspect the landing gear.

Townsville Airport is a used by both military and commercial aircraft.