A Qantas Airbus A330-200 returned to Sydney shortly after it took off, after one of the three hydraulic systems on board suffered a leak.

The airline says in a statement that it is now cooperating with the Australian Transport Safety Bureau (ATSB) in investigations into the incident, which left at least two passengers injured. It is also in communication with Airbus about the incident, and will launch its own investigations.

The aircraft, registered VH-EBC, was bound for Perth from Sydney, operating flight QF575.

Qantas says the flight crew noticed an alert for the hydraulic system 20 minutes after take-off and elected to return to Sydney. It stressed that “no emergency was declared”.

“Once the aircraft was back on the gate there were reports of a thick haze in the cabin, likely caused by hydraulic fluid entering the air conditioning unit,” says the Oneworld carrier, adding that there was no fire, even as some passengers may have thought it to be smoke.

Passengers were evacuated from emergency slides and via aerobridge into the the airport terminal.

Of the 221 passengers and 12 crew members on board, Qantas says two passengers were taken to hospital “for injuries sustained from using the slides”. A third was also taken to hospital “as a precaution”.

Media reports from Australia state some passengers noticing a burning smell from the aircraft, and that it took a while for the aircraft to be parked at an airport gate.

Cirium fleets data indicates VH-EBC was delivered to Qantas in 2003.

Story updated with figures from Qantas.