A Qantas plane was forced to make an emergency landing after a passenger suffered a suspected heart attack during the flight.

The Airbus A380 flight QF9 was en route from Melbourne to London on Friday when it descended into the gulf state of Oman.

The passenger died before the jet landed.

"The plane started to make a very fast descent and then later the pilot confirmed that they were making an emergency landing in Muscat, Oman," a fellow passenger told the Sydney Morning Herald.

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"He died before they could land and when they landed a string of people came on board to examine the situation.

"About an hour later they removed the body and distraught wife and travelling companions."

Qantas confirmed the emergency landing was due to a medical emergency.

The flight was delayed for four hours.