The engine of a British Airways plane which burst into flames during take-off was found to have "multiple breaches" in its casing, investigators have said.
In an initial report into the fire, the US's National Transportation Safety Board (NTSB) found parts of the engine flew out on to the runway.
The London-bound Boeing 777-200 caught fire as it was taking off at a Las Vegas airport on Wednesday, forcing 157 passengers, 10 crew and three pilots to evacuate down emergency slides.
The plane's left engine - a General Electric GE90-85B - its fuselage and wing were "substantially damaged" by the fire, according to the NTSB.
In a statement, investigators said: "Initial examination of the left engine revealed multiple breaches of the engine case in the area around the high pressure compressor.
"Examination of the material recovered from runway found several pieces of the high pressure compressor spool (approximately 7-8in in length)."
Flight data and cockpit voice recorders are being analysed while the engine will be taken away for a full examination.
Dr Colin Brown, from the Institution of Mechanical Engineers, said the NTSB report showed there were two potential causes of the engine failure.
He told the Press Association: "The engine problem was in the high pressure compressor, which points us towards two things that might have gone wrong.
"One is that it failed because of age or it failed because it ingested something - it may have picked up something from the runway."
Dr Brown said the investigators would examine the parts found on the runway for signs of fatigue while the possibility of something going into the engine would be considered by looking for marks on its front fan.
General Electric issued a statement which read: "The investigation is in its early stages, and it is premature to speculate or discuss any preliminary findings.
"Investigators continue to work to determine the sequence of events that led to the damage of the aircraft and engine."
Aviation safety expert David Learmount said the initial report confirmed the engine suffered an "uncontained failure".
He said: "We shouldn't treat this as a unique incident and say General Electric is to blame. Other engine manufacturers have had uncontained engine failures.
"Most of the time you get an engine failure the casing does contain the effects but sometimes it doesn't.
"It's an issue of balance. You could make it twice as thick and twice as heavy, but air fares would go up and more fuel would be used.
"You could make it like a tank but it wouldn't get off the ground."
One of the most serious incidents of an uncontained engine failure involved a Qantas London to Sydney superjumbo in November 2010 with 440 passengers on board.
Rolls-Royce admitted it had ''clearly fallen short'' of the highest standards following the dramatic disintegration of its engine, forcing the Airbus A380 to make an emergency landing shortly after take-off following a refuelling stop at Singapore.
An investigation into another emergency found that aircraft technicians for a flight which was forced to conduct an emergency landing in May 2013 at Heathrow might have been fatigued.
The BA Airbus A319 returned to the airport with smoke billowing from one of its engines, minutes into its flight to Oslo, Norway.
The Air Accidents Investigation Branch (AAIB) report said doors on both engines had been left unlatched during maintenance.
The aircraft suffered a punctured fuel pipe and a fire in the right engine.
BA issued a statement which said the Las Vegas incident happened after the plane ''experienced a technical issue''.
The aircraft was travelling between 40 and 100mph ahead of the 10-hour flight to Gatwick when the captain slammed the brakes on.
Twenty-seven people, including all crew members, were taken to hospital with minor injuries, mostly caused by sliding down the inflatable chutes to escape.
BA would not reveal how many of the passengers were British, although the Las Vegas to Gatwick route is popular with UK leisure travellers.