A Virgin plane has made an emergency landing at Melbourne Airport after an unusual odour was detected on board.

The plane, carrying 129 passengers to Sydney, was forced to return to Tullamarine airport just before 9am (AEDT) on Tuesday, a Virgin Australia spokeswoman said.

"The pilot returned to Melbourne as standard operating procedure after an unusual odour was detected in the cabin on the aircraft," she said.

The spokeswoman said the landing was a precautionary measure and passengers would travel on later flights.

An airport spokeswoman said a full emergency procedure had been declared but the plane landed safely and the pilot required no further assistance.