Passengers waiting for Qantas flights to London from Sydney — as well as others to and from Denpasar — have been left stranded in two locations around the world.

A Qantas recovery flight is still on its way to Baku, the capital of Azerbaijan, after its QF1 flight on its way from Sydney to London via Singapore was forced to make an emergency landing there on Saturday.

Qantas said its engineers were on their way to Baku from London to inspect the stranded Airbus A380 plane, with a suspected faulty fire sensor in the cargo hold to blame.

Passengers stuck at an airport hotel in Baku took to social media saying they did not expect a flight until late Christmas Eve, with more than a 24-hour delay ruining their Christmas plans.

In a statement issued on Saturday afternoon, a Qantas spokesman said the recovery flight to pick up the stranded passengers in Baku had left Sydney Airport just before noon.

"The recovery flight, which is being operated by an Airbus A380, departed Sydney at 11:40 this morning, [bound] for Baku Airport.

"The aircraft will then pick up customers at Baku Airport and continue on to London. It is expected to arrive at Heathrow early on Christmas morning."

The spokesman said passengers were also waiting in London's Heathrow Airport for the Baku recovery flight plane to be turned around for them to travel to their intended destinations.

He said that aircraft would take passengers back to Sydney, via Singapore, on QF2.

Qantas has apologised for the delay.

"We know this has been a significant disruption for customers ahead of Christmas, however, we will always put safety before schedule.

"We have apologised and thank [affected passengers] for their patience while we finalised the recovery plans.

"They have spent the night at the Marriott Hotel and been provided meals and transport. We're providing regular updates to customers on the recovery plan."

Passengers also stranded in Bali

Meanwhile, there have been major delays between Bali and Sydney, with both QF43 flight from Sydney to Denpasar, and QF44 flight from Denpasar to Sydney severely impacted.

A Qantas spokesman said bad weather in Bali yesterday meant the plane from Sydney had to be diverted to Jakarta Airport.

He said as the crew had reached their "tour of duty limit", meaning they had to be rested, causing a 24-hour delay to passengers waiting for the same plane to return back to Sydney from Denpasar on the QF44 leg.

Passengers vented their anger on social media, saying they had received little or no notice, with their Christmas travel plans badly delayed as a result.

Qantas says QF44 from Denpasar to Sydney was expected to leave on Saturday night, with passengers given hotel accommodation while waiting.