A Qantas flight bound for Perth has been forced to return to Sydney Airport after an issue emerged shortly after takeoff.

Passengers on a Qantas flight from Sydney to Perth have evacuated via slides after the Airbus A330 was forced to return as the cabin filled with smoke.

The flight was forced to turn back after an issue with the plane's hydraulics shortly after takeoff.

Qantas flight QF575 took off from Sydney Airport at around 8.45am (AEDT) Sunday morning.

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It was forced to return to the airport after the issue was detected, touching back down shortly before 9.30am.

The plane landed safely but was unable to taxi and had to be towed to the gate.

"Once back at the gate, the captain made the decision to evacuate the aircraft as a precaution and three emergency slides were deployed," the airline said in a statement.

"Passengers were evacuated through both the slides and normal exits."

One passenger described the incident on Twitter as "terrifying".

At least one passenger reported the cabin filling with "pungent" smoke before passengers were told to evacuate.

Emergency slides were deployed for passengers evacuating the plane. Photo / Dillon Parker, Twitter
Emergency slides were deployed for passengers evacuating the plane. Photo / Dillon Parker, Twitter

"Initially it was just the smell, we could smell something but after a few minutes this fume starting building up in the cabin," Sydney mechanic Rahman Akbari, 23, told the Daily Telegraph.

He said the captain appeared calm but it was a "little bit" scary when the crew began yelling "evacuate, evacuate" on the tarmac.

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Engineers are now inspecting the aircraft.

But the emergency return to Sydney Airport may have in fact saved a life.

Flight industry veteran Clifton Brock told the Daily Telegraph he had been flying to Perth to care for his 97-year-old mum.

She called him after the unexpected landing to say she needed an ambulance, and the former aviation worker advised her to use a medical emergency button.

The call wouldn't have come through if her son had been in the air, as he would have been had the flight not returned to Sydney.

He said the plane "did a short landing and hit the brakes really hard".

"It was really fast, everyone had to be out in 90 seconds," he said.

Qantas said it will release more information later today.

A Qantas flight bound for Perth has been forced to return to Sydney Airport after an issue emerged shortly after takeoff. Photo / Supplied
A Qantas flight bound for Perth has been forced to return to Sydney Airport after an issue emerged shortly after takeoff. Photo / Supplied

Several people were assessed by NSW Ambulance officers at the scene, but it's understood there are only minor injuries.

One patient has been taken to Royal Prince Alfred Hospital.

At least some stranded Qantas passengers have now been placed on replacement flights to Perth.