The A330-200 aircraft bound for Osaka was due to take off from Sydney International Airport at 11.30am (AEST) today, a Jetstar spokesman told AAP.

"A hydraulic-related issue meant we had to ask passengers to disembark," he said.

"Qantas engineers are addressing the problem."

Passengers boarded a replacement aircraft which was due to depart for Japan at 2pm (AEST).

The problem for Jetstar, a Qantas subsidiary, came after an incident earlier today when fumes appeared in the cabin of a Qantas passenger flight due to leave Melbourne for Sydney. Its 220 passengers were asked to disembark and the aircraft was taken out of operation.

And, in another incident, passengers booked on a Qantas flight to London were stranded overnight in Melbourne after the discovery of damage to the plane's wing.

Qantas said QF29, scheduled to leave Melbourne at 10.50pm (AEST) yesterday, was delayed after an access panel on the wing was damaged prior to boarding. The panel had been removed to service a component behind it.

The plane with 308 passengers took off at 6.12am today.