A Qantas recovery flight deployed from Sydney has landed in Azerbaijan to pick up stranded Qantas passengers, and is expected to deliver them to London by Christmas morning local time, the airline has said.

The replacement A380 aircraft left Sydney at 11:40am Saturday and arrived at Baku International Airport early on Sunday morning.

The flight will depart later today and continue on to London arriving "early on Christmas morning", Qantas announced in a statement.

The passengers were on flight QF1 from Singapore to London, which was forced to make an emergency landing on Friday.

Passengers stuck at the Marriott airport hotel in Baku had earlier taken to social media saying the more than a 24-hour delay had ruined their Christmas plans.

Qantas said a suspected faulty fire sensor in the cargo hold was to blame.

An airline spokesman said passengers were also waiting in London's Heathrow Airport for the Baku recovery flight plane to return passengers to Sydney, via Singapore.

Qantas 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."

Bali flight lands in Sydney

Another Qantas flight with Australians on board touched down in Sydney on Sunday morning, after bad weather trapped them in Bali. 

The QF44 flight from Denpasar was delayed on Friday after the plane from Sydney had to be diverted to Jakarta Airport due to poor weather.

Qantas said there was a 24-hour delay, as crews had to be rested before completing the return trip back to Sydney.

The flight landed in Sydney around 8:20am Christmas morning.