The QF94 service was two hours into its trip on Friday evening when the pilot was forced to abort the flight, with passengers saying sparks were seen coming from one of the four engines.
"@Qantas Flight94 to Melb returned to LAX with sparks coming from an engine & now being inspected," tweeted passenger RobD.
Qantas said the sparks may have been from the engine overheating but denied reports in Australia that it caught fire.
"Friday night's QF94 A380 service from Los Angeles to Melbourne turned back to LA because of an issue with one of the aircraft's four engines," the airline said in a statement.
"Engineers are inspecting the aircraft."
Passengers were put on a replacement flight, with the Australian Transport Safety Bureau notified about the incident.
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