Footage shows terror on board as flight announces emergency landing. [Representational Image]Creative Commons

A Qantas flight from Perth to Sydney announced a sudden emergency landing after experiencing problems mid-air with its air conditioning system.

Qantas flight 568 was diverted to Melbourne and landed safely at Tullamarine at 6.17 am Saturday.

Footage uploaded by 7 News Sydney shows the passengers wearing an oxygen mask while the announcement goes on saying: "Sit down in the nearest seat now and pull down an oxygen mask."

According to reports, the problem with the air conditioning affected the aircraft's ability to "maintain pressure in the cabin." The aircraft with almost 300 passengers was part-way across the Nullarbor when it was diverted to Melbourne.

"Following standard procedure, the crew descended to 10,000 feet and were able to restart the system and diverted to Melbourne," Qantas said in a statement.

The flight descended to 10,000 feet, where pressurization is not required. One of the passengers on board, Ray Chant, took out his mobile phone to get prepared for the worst, "Terrified. I just thought, how can I record this and say my last goodbyes?" he told 7 News.

Paramedic Sam Pumphrey said that she did whatever she could to calm those around her. "Because everyone was freaking out, hyperventilating," she said. "There was a couple, a young lady struggling big time."

Some passengers said that there was a smell of burning plastic moments before the emergency descent, but finished with a safe landing in Melbourne. Passengers were heard cheering and clapping in footage after the landed safely.

Pumphrey believes that there was one positive outcome from all that happened. She said:"A lot of us are very close now....considering the situation we've been through."

The passengers were being redirected to Sydney on the first available flights after landing. According to Qantas, its engineers are assessing the aircraft, which for now remains grounded.