SYDNEY, AUSTRALIA - A Qantas flight from Singapore to London was diverted to the German city of Frankfurt on Sunday due to engine troubles, the Australian airline said.

The Boeing 747-400 aircraft changed its route due to 'the captain being alerted to a vibration in one of the engines,' a Qantas spokeswoman said.

'As is standard procedure the engine was shut down,' she told the national news agency AAP.

'There was no safety issue at any time and the aircraft continued to Frankfurt, where it landed without incident.'

Qantas, already battling a wave of bad publicity after a mid-air blast caused by an exploding oxygen cylinder blew a hole in a jet en route to Melbourne in July, said it was investigating the engine problem.

Passenger Andrew Negline told the Australian Broadcasting Corporation that many passengers were woken by a loud noise before an announcement that the plane would be diverted.