* China Eastern flight makes emergency return to Sydney
* Gaping hole seen in casing of one engine
* "I was really scared. Our group was terrified" - passenger (Adds comments from Rolls-Royce, aviation expert, airline, passengers, details, paragraphs 2, 5-7, 11-12; changes dateline to SYDNEY)
SYDNEY, June 12 (Reuters) - A China Eastern flight bound for Shanghai was forced to turn back to Sydney due to a mid-air emergency, a spokeswoman for the airline said on Monday, with pictures showing a gaping hole in the casing of one of the plane's engines.
The plane, which data from flight tracking website FlightAware showed was an Airbus A330-200 twin jet, landed without incident and there were no injuries, said Kathy Zhang, a general manager at China Eastern Airlines.
"The crew observed the abnormal situation of the left engine and decided to return to Sydney airport immediately. All passengers and crew members were landed safely," she said.
Photographs published by several Australian media outlets showed a large gash well over a metre long in the casing of the plane's left engine.
A spokeswoman for Rolls-Royce, which manufactured the plane's Trent 700 series engines, said in a statement: "We are aware of the incident and will be working closely with our customer and relevant partners to understand the cause of the issue."
Professor Jason Middleton, an aviation expert at the University of New South Wales in Sydney, said it appeared that the engine cowling had been ripped away forward of the main compressor blade.
"When one of these things happens you often don't know how the damage began. It could have begun from loose screws," he told Australian Broadcasting Corp. News.
The Australia Transport Safety Bureau said it was investigating the incident.
China Eastern's Zhang said a comprehensive investigation would involve aviation authorities from Australia and China.
"The engine for the aircraft is a big issue so we need to investigate with the governments, with the Rolls Royce company and with our headquarters as well," she said.
Television station Seven News reported that passengers heard a bang shortly after Flight MU736 took off and could then smell burning before the flight turned back.
"We went up in the air and all of a sudden we heard this noise ... it kind of smelt like burning. Oh, I was scared. Yeah, I was really scared. Our group was terrified," one unidentified passenger told Seven News.
Another passenger, identified only as Eva, said the cabin crew tried to calm passengers and told them to fasten their seatbelts after a noise was heard.
"We were very panicked because we had no idea what was happening," she told Channel 9 television. (Reporting by Harry Pearl; Additional reporting by Charlotte Greenfield and Ana Nicolaci da Costa in WELLINGTON and Brenda Goh in SHANGHAI; Editing by Paul Tait)