A Qantas A380 plane has been forced to fly back to Singapore's Changi Airport after pilots found one of its engines malfunctioning and were forced to shut down.

Qantas Flight QF32 was bound for Sydney when the engine failed, reports from Reuters and the Sydney Morning Herald said.

"Qantas flight QF32 was en route from Singapore to Sydney, the number two engine has shut down, so as a precautionary measure we are taking it back to Singapore," a Qantas spokeswoman said in reports. She noted at 2.30pm AEDT, it would land in 40 minutes.

Qantas refuted reports that an explosion happened before landing.

Qantas Airways said that one of its planes had crashed on Thursday, saying a passenger flight had experienced engine trouble and was returning to Singapore airport.