Qantas passengers used emergency slides to evacuate a plane after it was forced to return to Sydney Airport following a "hydraulic issue".

Key points: A Qantas flight travelling to Perth on Sunday morning returned to Sydney 30 minutes after take-off

A Qantas flight travelling to Perth on Sunday morning returned to Sydney 30 minutes after take-off Some passengers received cuts and bruises during the evacuation process

Some passengers received cuts and bruises during the evacuation process Qantas said the incident was caused by a "leak of hydraulic fluid"

The Sydney to Perth flight QF575, an Airbus A330-200 which carries up to 271 passengers, took off at 8:45am on Sunday.

About 20 minutes into the flight, the captain announced the plane had to turn around due to mid-flight hydraulic issues.

Passengers told the ABC the plane was stuck on the tarmac after landing when what appeared to be smoke began to fill the cabin.

"We were on the runway waiting to be towed in and we started to smell burning," Dillon Parker, who is holidaying in Australia from Scotland, said.

One passenger described it as a "terrible smell".

Passengers were forced to evacuate the plane via the emergency slides. ( Supplied )

Passenger Ally Kemp, who was on the last leg of a trip to Perth after spending six months studying overseas, said the scene was "terrifying".

"When we got back to the gate, the cabin started to fill with smoke and basically the captain started screaming 'Evacuate!'," the 20-year-old said.

"It took a few seconds to sink in and then basically it was a mad scurry to go down the slides and get off the plane which was just crazy."

Qantas Captain Debbie Slade said there had been a "leak of hydraulic fluid" which affects landing controls and flaps on the aircraft.

"I think perhaps some of the hydraulic fluid was pumped in by the air-conditioning system," she said.

"I haven't heard of any indications of smoke. It may have appeared like smoke but it was mist from the hydraulic system."

Captain Slade said some of the passengers may have had "itchy eyes" or a "scratchy throat" from exposure to the fluid.

During the dash for the exit, some people said they received injuries to their arms and legs as they were pushed by other panicking passengers.

Others had slammed their heads against the overhead luggage compartment as they jumped out of their seats.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 36 seconds 2 m 36 s 'Potentially catastrophic,' 'stressful': passengers tell of being evacuated from Qantas flight ( ABC News )

Niamh Champion had carried her 10-month daughter down the emergency slide, while her three-year-old son followed closely behind.

She said the delay was frustrating but safety was more important.

"There was a real genuine problem with the hydraulics and had we continued onto Perth, that could've been potentially catastrophic," she said.

In a statement, Qantas said engineers were inspecting the aircraft after the evacuation.

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

NSW Ambulance said "all patients had been evacuated" with one passenger being taken to Royal Prince Alfred Hospital for "minor injuries".

Others were treated for bruises and cuts at the scene.