A Jetstar aircraft was met by fire trucks at Sydney Airport after a strange smell was reported in the cabin.
Flight JQ517 was en route to Melbourne when cabin crew reported a strange odour at the rear of the plane, about 20 minutes out of Sydney.
A spokesman for the airline told 7 News the captain had decided to return to Sydney as a precaution. The plane landed at around 2.30pm and was surrounded by emergency services.
Passenger Rachel Bale told 7 News those on board were told very little about what was happening.
"There was very little communication to passengers. No one knew what was going on," she said. "The pilot was very vague and called it 'an indication' that we had to return to Sydney"
Passengers stayed on the plane as firefighters investigated the incident.
"They looked to be measuring the air," Bale said. "I was pretty nervous and just wanted to get off the plane."
The origin of the odour has not yet been determined.
The Jetstar spokesman said the airline was working to re-organise flights for those affected and had a spare jet in Sydney.
Major delays were not expected, he said.