A Qantas flight from Sydney to Buenos Aires has had to turn back due to technical problems.

Airline spokeswoman Olivia Wirth says the captain on flight QF17 decided to return to Sydney one hour into the flight after smoke entered the cockpit.

She says the plane will be assessed to work out the nature of the problem, thought to be in the plane's electrical system.

"Engineers are inspecting the aircraft and they're trying to determine the cause... and make sure we can have the aircraft back in the air as soon as possible," Ms Wirth said.

The Boeing 747 landed without incident at Sydney airport about 1:20pm (AEDT).

Ms Wirth says the captain had requested priority to land after turning around and dumping fuel.

In a statement the company said reports that the plane lost cabin pressure were untrue. Oxygen supply to the cabin was unaffected, it added.

The airlines says all 199 passengers and the 21 crew are safe and the company is making contingency arrangements for them.

It is not known if the affected passengers will fly again this evening or if they face a longer delay.

Earlier this month a Qantas plane's engine exploded over Indonesia.

Qantas and Singapore Airlines grounded their A380 planes while the cause of the explosion was investigated.

A day later, a Qantas Boeing 747 was forced to turn back from Singapore en route to Sydney because of a "contained engine failure".

On Friday a Qantas 767 en route to Melbourne turned back to Perth after vibrations were detected in one of its engines.

Qantas says it regrets any inconvenience caused to those affected by the latest incident.

While Qantas faces continuing questions over the reliability of the engines on its A380 fleet, the company's budget airline, Jetstar, is also having to defend its safety record.

Jetstar does not operate any A380s but it faces a Senate inquiry next month into aviation and flight safety standards just as it is launching a major expansion into Asia to exploit the Chinese consumer market.

Chief executive Bruce Buchanan was not shying away from the association with Qantas when he spoke to ABC business editor Peter Ryan.

"Qantas's reputation is a positive not a negative... we would therefore like the association with Qantas, especially the fact that we have very similar safety standards across both businesses."