Sydney: Engine failure which blasted a hole in a Sydney-bound Qantas jet carrying 212 people forced it to return to San Francisco, the Australian airline said on Wednesday.

Passengers told Australian media that the plane shook and flames were seen coming out of the affected engine early into the Boeing 747-400's flight from San Francisco late on Monday.

"It wasn't turbulence, it seems that there was some pretty serious damage," one passenger told Channel Nine.

"I could see the flames and all these sparks coming off it and also felt the eruption when it exploded," another said.

Qantas said investigations were under way into the incident, which it said occurred about 15 minutes into the flight when the crew detected "excessive vibration" in one of the plane's four Rolls Royce engines.

Staff shut down the engine and sought priority clearance to return to San Francisco, spokesman Simon Rushton said.

The flight, which was also carrying 18 crew, dumped fuel before landing without incident, he added.

"Initial engineering checks on the ground confirmed that the engine had failed," Rushton said.

"We are still in the early stages of investigations in terms of ascertaining what caused the failure.

"There are a couple of what you might describe colloquially as holes in the engine. That's part of the indication that the engine had failed," he added.
Qantas said no-one was injured in the incident, adding that safety was the airline's number one priority.

"The fact is, very occasionally engines do fail on aircraft and in fact it's a testament to the skill of our engineers and our flight crew that they would bring this aircraft home quite safely," spokesman David Epstein told ABC.

But the association for aircraft maintenance engineers said it was fortunate nobody was injured by debris flying from the engine.