SYDNEY • A China Eastern Airlines passenger plane has made an emergency landing in Sydney after a huge hole appeared in one of its engine casings and forced it to turn back just after taking off.

Terrified passengers described a very loud noise soon after Flight MU736 left Sydney Airport for Shanghai at 8.30pm on Sunday.

The crew cleared seats near the affected engine and turned the flight back. No one aboard the twin-engine Airbus A-330 was injured.

China Eastern said the crew found damage in the casing of the air inlet in the left engine, as photographs published by several Australian media outlets showed a large gash well over a metre long.

"The crew... decided to return to Sydney Airport immediately," an airline spokesman said in an e-mail.

"The returned aircraft is currently under investigation at Sydney Airport."

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."

Another passenger, identified only as Eva, said the cabin crew tried to calm passengers and told them to fasten their seatbelts after the noise was heard.

"We were very panicked because we had no idea what was happening," she told Channel 9 television.

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 A-330. In that incident, take-off was aborted at the last minute as the plane was accelerating for departure on the runway.

Mr Thomas said the panel of the China Eastern plane might have come loose and been sucked into the engine. He said an Airbus airworthiness directive issued in 2011 and updated in 2014 noted that some operators had found that acoustic panelling in the cowling area - or removable cover - was disbonding.

"It was a problem 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... it's their responsibility."

Ground-handling company Ca- thay Pacific had inspected the plane before take-off, said Ms Kathy Zhang, China Eastern's general manager for the Oceania region. "The engine for the aircraft is a big issue so we need to investigate with the governments, with the (engine maker) Rolls-Royce company and with our headquarters as well," she said.

Mr Thomas 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, he said the damage was not as severe as the engine failure experienced by Qantas in 2010 owing to a separate problem, which led the carrier to ground all its A-380s. The Qantas A-380 was on its way from Singapore to Sydney when a mid-air explosion shattered one of its engines.

AGENCE FRANCE-PRESSE, REUTERS