Report from Channel 9 news:
Air Canada plane lands safely in Sydney
Some extracts:
"Air Canada reported smoke in the cabin and conducted a fuel dump," the ATSB spokesman told AAP.
He said the incident would be investigated further.
A spokesman for Sydney Airport told AAP said the plane was doing an "air return".
"It's doing an air return... an air return usually means they are coming back as a precaution," he said on Thursday.
Air Canada's general manager for Australia and New Zealand, Jeannie Foster, said there was smoke in the plane but no fire.
"There was some smoke seen in the cabin by the crew, actually it was coming from the oven," she told Macquarie Radio.
"It was just smoke coming from an oven, there were no injuries."
There were 264 passengers on board the flight, including four infants.
"The captain didn't declare an emergency," Ms Foster said.
"Obviously he has had to dump fuel as it is a 15 hour flight to Canada... and you can't land with a heavy plane."