Terrified passengers described a very loud noise soon after flight MU736 left Sydney Airport for Shanghai at 8.30pm (1030 GMT) on Sunday.

Crew cleared seats near the affected engine and turned the flight back. No one aboard the twin-engine Airbus A330 was injured.

China Eastern said the crew found damage in the casing of the air inlet in the left engine.

“The crew… decided to return to Sydney Airport immediately,” an airline spokeswoman added in an emailed statement to AFP.

“The returned aircraft is currently under investigation at Sydney Airport.”

Images posted on social media showed a large hole ripped in the casing.

An unidentified passenger told broadcaster Channel Seven: “We, like, went up in the air and all of a sudden, I heard like ‘z-z-z-z-z’ and it was really, really loud. It kind of smelled like burning.

“Oh, I was scared. Yes. I was really scared. Our group was terrified.”

Another passenger told Channel Nine that “the wing to my left just started making a massive amount of noise and they cleared all of the seats”.

– Panel detached? –

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AirlineRatings.com editor Geoffrey Thomas said investigators would be looking at whether the acoustic panelling of the engine had become detached, citing a similar incident in mid-May involving an Egypt Air A330.

He said the panel might have come back and been sucked into the engine.

Thomas said an Airbus airworthiness directive issued in 2011 and updated in 2014 noted that some operators had found acoustic panelling in the cowling area was disbonding.

“It was a problem that they knew about and airlines had been warned and had been required to inspect their engines and if necessary replace the panels,” he added.

“Whoever is looking after the maintenance of the engines, whether it is the airline or the engine maker, it’s their responsibility.”

He said the China Eastern incident was unusual and the serious damage to the engine meant it was likely to be replaced.

But despite the dramatic scenes, Thomas said the damage was not as severe as the engine failure experienced by Qantas Singapore-Sydney flight QF32 in 2010 due to a separate problem, which led the Australian carrier to ground all its A380s.

The robustness of today’s engines also meant twin-engine jets could continue taking off — when they were under the most stress — even if there was a failure of one of them, he said.

“Engines today are so reliable that in fact some twin-engine aeroplanes are certified to fly up to 330 minutes flying time away from an alternate airport,” Thomas said.

China Eastern said all passengers would be placed on flights departing Australia Monday.