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A Qantas jetliner has made an emergency landing in Singapore with 459 people aboard, after one of its four engines shut down over western Indonesia.

The landing came following witness reports of a blast that sent debris hurtling to the ground and after it was widely reported the aircraft had crashed.

The plane landed with smoke emitting from its underside, according to an AFP reporter at Changi airport.

Six fire engines surrounded the plane as it hit the tarmac.

Qantas has told the Associated Press an Airbus A380 carrying 433 passengers and 26 crew touched down safely after mid-air trouble.

Indonesian media reports today said there had been some sort of explosion over the Indonesian island of Batam, near Singapore, at about 9.15am local time.

Tatang Kurnia, head of Indonesia's Transportation Safety Board, said the explosion came from a Qantas plane that had just lifted off from Singapore.

"We've been informed from Singapore that a Qantas plane overflying the area defuelled and then made an emergency landing back in Singapore," he told MetroTV.

Qantas denies explosion

But Qantas has denied there was any explosion, and said the plane landed safely with no injuries. Qantas had no immediate comment on whether the engine troubles were related to eruptions of Indonesia's Mount Merapi over the past 10 days.

Given the timing of the malfunction, 15 minutes after takeoff from Singapore, and the airliner's flight path, there appeared to be no connection.

"Qantas flight QF32 was enroute from Singapore to Sydney, the number two engine has shut down, so as a precautionary measure we are taking it back to Singapore," a Qantas spokeswoman told AAP.

The initial reports that the plane had crashed sent Qantas' shares lower but they later recovered.

The flight originated in London and had taken off from Singapore heading for Sydney.

Qantas spokeswoman Emma Kearns told the Associated Press the plane could safely fly on three engines, but that the pilot landed the plane to be safe.

Kearns said there have been no reports of injuries and that the airline had not received any reports of an explosion on board.

Not known if problems linked to volcano

When asked if the engine trouble was related to ash hurled from Merapi, Kearns said she had no further details.

A series of powerful eruptions from Indonesia's most volatile volcano, which was spewing massive clouds of gray ash 1,400km west of Batam, earlier prompted officials to close some air routes above the mountain.

"We have no way of knowing what at this point caused the problem," said Tatang Kurniadi, the chief of The National Transportation Safety Committee, when asked if there were fears volcanic ash clogged the Qantas airliner's engine.

Police and witnesses said they heard an explosion as the plane was flying over western Indonesia and found debris from the plane scattered near a shopping mall on the island of Batam.

Debris likely to be engine cowling

Large pieces of debris - including panels painted white and red - were found on the Indonesian island of Batam, where witnesses reported hearing the loud bang.

Pictures of metal, some the size of a door, flashed on MetroTV, with people milling around.

"I heard a big explosion at around 9:15 a.m. and saw a commercial passenger plane flying low in the distance with smoke on one of its wings," Rusdi, a local resident, told MetroTV.

"The debris started falling on my house."

Australian aviation expert Ian Holland says pictures of the debris that reportedly fell from the plane is "almost certainly part of the engine cowling".

Mr Holland told Sky News that the cowling acts like a bonnet on a car in that it covers an engine.

According to Mr Holland, the loss of a cowling is "certainly nothing that would affect the integrity of the aircraft".

Despite reports of an explosion on board, Mr Holland said a number of issues could have caused the cowling to come loose.

"It could quite possibly have been a malfunctioning hinge," he said "There may not have been an explosion at all - it's too early to tell.

"If it was a large mechanical failure, you would have seen a lot more debris."

Batam is in the Riau Islands province of Indonesia, located 20km off Singapore's south coast.

- AP, AAP, NZ Herald staff